Cognitive Biases

Cognitive biases describe the irrational errors of human decision making and they are a crucial part of understanding behavioral economics.

These scientific human biases affect the way we shop, invest and judge brands and people.

The revolutionary study of cognitive biases led Daniel Kahneman to win the Nobel Prize and opened the rapidly expanding field of behavioral economics.

By understanding cognitive biases, you will be able to read your customers’ minds better and design your product or marketing strategy accordingly.

In this list of cognitive biases, I try to explain the basic idea behind every bias in a plain non-academic language with simple examples.

Let’s begin…

Affect Heuristic

A mental shortcut that allows people to make decisions quickly by bringing their emotional response into play. They make decisions according to their gut feeling.

Researchers have found that when people have a pleasant feeling about something, they see the benefits as high and the risks as low, and vice versa.

As such, the affect heuristic behaves as a first and fast response mechanism in decision-making.

For example, if someone has harmed you, you quickly arrive at the conclusion that this person is cold and unfriendly. If fact, even if the person didn’t harm you on purpose, you may still about him or her the same.


A cognitive bias that describes the human tendency to rely too heavily on the first piece of information offered (the “anchor”) when making decisions.

For example, an initial price offered for a used car sets the standard for the rest of the negotiation.

Availability Heuristic

A mental shortcut that relies on immediate examples that come to a given person’s mind when evaluating a specific topic, concept, method or decision.

People tend to heavily weigh their judgments toward more recent information, making new opinions biased toward the latest news.

For example, which job is more dangerous – being a police officer or a logger? While high-profile police shootings might lead you to think that cops have a more dangerous job, statistics actually show that loggers are more likely to die on the job than cops.

This illustrates that availability heuristic helps people make fast, but sometimes incorrect assessment.

Bounded Rationality

The idea that in decision-making, people are limited by the information they have, the cognitive limitations of their minds, and the finite time. As a result, they seek for a “good enough” decision and tend to make a satisficing (rather than maximizing or optimizing) choice.

For example, during shopping when people buy something that they find acceptable, although that may not necessarily be their optimal choice.

Certainty Effect

When people overweight outcomes that are considered certain relative to outcomes that are merely possible.

The certainty effect makes people prefer 100% as a reference point relative to other percentages, even though 100% may be an illusion of certainty. Lower percentages or probabilities can be more beneficial in the long run.

For example, people prefer a 100% discount on a cup of coffee every 10 days to other more frequent but lower discount offer, even though the second option may save them more money in the long run.

Choice Overload

A cognitive process in which people have a difficult time making a decision when faced with many options.

Too many choices might cause people to delay making decisions or avoid making them altogether.

For example, a famous study found that consumers were 10 times more likely to purchase jam on display when the number of jams available was reduced from 24 to 6.

Less choice, more sales. More choice, fewer sales.

Cognitive Dissonance

A mental discomfort that occurs when people’s beliefs do not match up with their behaviors.

For example, when people smoke (behavior) and they know that smoking causes cancer (cognition).


The tendency to be consistent with what we have already done or said we will do in the past, particularly if this is public.

For example, researchers asked people if they would volunteer to help with the American Cancel Society. Of those who received a cold call, 4% agreed. A second group was called a few days prior and asked if they would hypothetically volunteer. When the actual request came later, 31% of them agreed.

Confirmation Bias

The tendency to search for or interpret information in the way that confirms one’s preexisting beliefs, leading to statistical errors.

When people would like a certain idea to be true, they end up believing it to be true. They are motivated by wishful thinking.

For example, a person with a low self-esteem is highly sensitive to being ignored by other people, and they constantly monitor for signs that people might not like them.

Decision Fatigue

A lower quality of decisions made after a long session of decision making.

Repetitive decision-making tasks drain people’s mental resources, therefore they tend to take the easiest choice – keeping the status quo.

For example, researchers studied parole decisions made by experienced judges and revealed that the chances of a prisoner being granted parole depended on the time of the day that judges heard the case.
65% of cases were granted parole in the morning and fell dramatically (sometimes to zero) within each decision session over the next few hours. The rate returned back to 65% after a lunch break and fell again.

Decoy Effect

People will tend to have a specific change in preferences between two options when also presented a third option that is asymmetrically dominated.

In simple words, when there are only two options, people will tend to make decisions according to their personal preferences. But when they are offered another strategical decoy option, they will be more likely to choose the more expensive of the two original options.

For example, when consumers were offered a small bucket of popcorn for $3 or a large one for $7, most of them chose to buy the small bucket, due to their personal needs at that time.
But when another decoy option was added – a medium bucket for $6.5, most consumers chose the large bucket.

Dunning-Kruger Effect

A cognitive bias in which people who are ignorant or unskilled in a given domain tend to believe they are much more competent than they are.

In simple words, “people who are too stupid to know how stupid they are”.

For example, a nationwide survey found that 21% of Americans believe that it’s ‘very likely’ that they’ll become millionaires within the next 10 years.

Time Discounting / Present Bias

The tendency of people to want things now rather than later, as the desired result in the future is perceived as less valuable than one in the present.

When offered a choice of $100 today (SSR – smaller sooner reward) and $100 in one month, people will most likely choose the $100 now.
However, if offered a choice of $100 today (SSR) and $1000 in one month (LLR – larger later reward), people will most likely choose the $1000.

The challenge is to find the point where people value the SSR and the LLR as being equivalent.

For example, a research found that a $68 payment right now is just as attractive as a $100 payment in 12 months.

Diversification Bias

People seek more variety when they choose multiple items for future consumption than when they make choices sequentially on an ‘in the moment’ basis.

For example, before people are going on vacation, they add classical, rock and pop music to their playlist but eventually end up listening to their favorite rock music.

Ego Depletion

People have a limited supply of willpower, and it decreases with overuse. Willpower draws down mental energy – it’s a muscle that can be exercised to exhaustion.

For example, a research showed that people who initially resisted the temptation of chocolates were subsequently less able to persist on a difficult and frustrating puzzle task. Additionally, when people gave a speech that included beliefs contrary to their own, they were also less able to persist on the difficult puzzle.


A decision-making technique. When people face with multiple options, they first identify a single feature that is most important to them. When an item fails to meet the criteria they have established, they cross the item off their list of options. Different features are applied until a single ‘best’ option is left.

For example, a consumer may first compare cars on the basis of safety, then gas mileage, price, style, etc, until only one option remains.

Hot-Cold Empathy Gap

We have trouble imagining how we would feel in other people’s shoes.

We are also not good at imaging how other people would respond to things because we assume they would respond in the same way we would.

For example, people post videos of their kids or bragging about their latest business success on Facebook assuming that their friends would appreciate it and be happy for them. Unfortunately, this often provokes negative feelings and makes their facebook friends resentful, angry or sad.

Endowment Effect

Once people own something (or have a feeling of ownership) they irrationally overvalue it, regarding of its objective value.

People feel the pain of loss twice as strongly as they feel pleasure at an equal gain, and they fall in love with what they already have and prepare to pay more to retain it.

For example, scientists randomly divided participants into buyers and sellers and gave the sellers coffee mugs as gifts. Then they asked the sellers for how much they would sell the mug and asked the buyers for how much they would buy it.

Results showed that the sellers placed a significantly higher value on the mugs than the buyers did.

Fear of Missing Out (FOMO)

An anxious feeling that can happen when you fear that other people might be having rewarding experiences that you’re missing.

Many people have been preoccupied with the idea that someone, somewhere, is having a better time, making more money, and leading a more exciting life.

According to science, FOMO is associated with lower mood, lower life satisfaction, and an increasing need to check social media.

Framing Effect

A cognitive bias, in which people react to a particular choice in different ways depending on how it is presented, as a loss or as a gain.

People tend to avoid risk when a positive frame is presented but seek risks when a negative frame is presented.

For example, people are more likely to enjoy meat labeled 75% lean meat as opposed to 25% fat, or use condoms advertised as being 95% effective as opposed to having a 5% risk of failure.

Gambler’s Fallacy (Monte Carlo Fallacy)

The mistaken belief that, if something happens more frequently than normal during a certain period, it will happen less frequently in the future, or that, if something happens less frequently than normal during a certain period, it will happen more frequently in the future.

For example, if you are playing roulette and the last four spins of the wheel have led to the ball’s landing on black, you may think that the next ball is more likely than otherwise to land on red.

In 1913 at the Monte Carlo Casino, the ball fell on the black of the roulette wheel 26 times in a row and gamblers lost millions betting against the black, thinking mistakenly that the next ball is more likely to land on red,  when in fact the odds are the same as they always were – 50:50.


A routine or behavior that is repeated and tends to occur subconsciously.

Habits are performed automatically because they have been performed frequently in the past.

Changing a habit is a process, not an event. According to science, it takes 66 days to form or change a new habit (and not 21 days like the old myth).

Halo Effect

A cognitive bias in which our overall impression of a person influences how we feel and think about his or her character.

We assume that because people are good at doing A, they will be good at doing B and C too.

Your overall impression of a person (“She is nice!”) impacts your evaluation of that person’s specific traits (“She is also smart!”).

Scientists also found that people tend to rate attractive individuals more favorably for their personality traits or characteristics than those who are less attractive.

Hedonic Adaptation

People quickly return to their original level of happiness, despite major positive or negative events or life changes.

When good things happen, we feel positive emotions but they don’t usually last. The excitement of purchasing a new car or getting a promotion at work is temporary.

One study showed that despite initial euphoria, lottery winners were no happier than non-winners eighteen months later.

Herd Behavior

The tendency for individuals to mimic the actions (rational or irrational) of a larger group. Individually, however, most people would not necessarily make the same choice.

For example, in the late 1990s investors were investing huge amounts of money into Internet-related companies, even though most of them did not have structured business models. Their driving force was the reassurance they got from seeing so many others do the same.

Hindsight Bias (Knew-It-All-Along Effect)

The tendency of people to overestimate their ability to have predicted an outcome that could not possibly have been predicted.

A psychological phenomenon is which people believe that an event was more predictable than it actually was, and can result in an oversimplification in cause and effect.

For example, after the great recession of 2007, many analysts explained that all the signs of the financial bubble were there. If the signs had been that obvious, how come almost no one saw it coming in real time?

IKEA Effect

A cognitive bias in which people place a disproportionately high value on products they partially created.

For example, in one study, participants who built a simple IKEA storage box themselves were willing to pay much more for the box than a group of participants who merely inspected a fully built box.

Less-Is-Better Effect

When low-value options are valued more highly than high-value options.

This effect occurs only when the options are evaluated separately. This way the evaluations of objects are influenced by attributes which are easy to evaluate rather those which are important.

For example, a research revealed that:

  • A person giving an expensive $45 scarf as a gift was perceived to be more generous than one giving a $55 cheap coat.
  • An overfilled ice cream serving in a small cup with 7 oz of ice cream was valued more than an underfilled serving in a large cup with 8 oz of ice cream.

Licensing Effect

When people allow themselves to indulge after doing something positive first.

Drinking a diet coke with a cheeseburger can lead one to subconsciously discount the negative attributes of the meal’s high caloric and cholesterol content.

Going to the gym can lead us to ride the elevator to the second floor.

study showed that people who took multivitamin pills were more prone to subsequently engage in unhealthy activities.

Loss Aversion

People’s tendency to prefer avoiding losses to acquiring equivalent gains. It’s better not to lose $5 than to find $5.

The pain of losing is psychologically about twice as powerful as the pleasure of gaining.

For example, scientists randomly divided participants into buyers and sellers and gave the sellers coffee mugs as a gift. They then asked the sellers for how much they would sell the mug and asked the buyers for how much they would buy it.

Results showed that the sellers placed a significantly higher value on the mugs than the buyers did. Loss aversion was the cause of that contradiction.

Mental Accounting

The tendency of people to divide their money into separate accounts based on subjective criteria, like the source of the money and the intent for each account.

For example, people often have a special fund set aside for a vacation, while carrying substantial credit card debt, despite the fact that diverting funds from debt repayment increases interest payments and reduces net worth.

Similarity, another study revealed that supermarket shoppers spent less money paying with cash than with credit cards. Comparing the price of goods to a smaller mental account (cash) than to a larger mental account (credit card) increased the pain of payment.

Naive Diversification

When people have to make several choices at once, they tend to diversify more than when making the same time of decision sequentially.

For example, when people ask to choose now which of six snacks to consume in the next three weeks, they pick more kinds of snacks than when they ask to choose once a week six snacks to consume that week for three weeks.

As a result, investors tend to think that by simply investing in a number of unrelated assets, a portfolio will acquire enough diversification to enjoy relative freedom from high risk and potential for profit.

Optimism Bias

A cognitive bias that causes people to believe that they are at a lesser risk of experiencing a negative event compared to others.

When it comes to predicting what will happen to us tomorrow, next week, or fifty years from now, we overestimate the likelihood of positive events.

For example, smokers tend to feel they are less likely than other individuals who smoke to be afflicted with lung cancer. Similarity, motorists tend to feel they are less likely to be involved in a car accident than is the average driver.

Research has also found that people show less optimistic bias when experiencing a negative mood, and vice versa.

Overconfidence Effect

We systematically overestimate our knowledge and our ability to predict.

Overconfidence measures the difference between what people really know and what they think they know.

It turns out the experts suffer even more from the overconfidence effect than laypeople do.

Studies have found that over 90% of US drivers rate themselves above average, 68% of professors consider themselves in the top 25 percent for teaching ability, and 84% of Frenchmen believe they are above-average lovers.

Overjustification Effect

The loss of motivation and interest as a result of receiving an excessive external reward (such as money and prizes).

When being rewarded for doing something actually diminishes intrinsic motivation to perform that action.

For example, researchers gave children reward for doing activities they already enjoyed, like solving puzzles. Then, the children were given an opportunity to engage in these same activities on their own, when no rewards would be forthcoming. The results: children engaged in these activities less often than they did before.

Pain of paying

Some purchases are more painful than others, and people try to avoid those types of purchases. Even if the actual cost is the same, there is a difference in the pain of paying depending of the mode of payment.

Purchases are not just affected by the price, utility and opportunity cost, but by the pain of paying attached to the transactions.

Studies show that people feel the pain of paying the most when they:

  • Paying in cash (as opposed to credit card).
  • Paying a separate fee/commission (as opposed to fee included in the total purchase price).
  • Paying as they consume (as opposed to one-time payment).
  • Paying frequently (as opposed to prepaid).
  • Paying on their own (as opposed to receiving a gift from their partners).


When the rate of consumption decreased by physically partitioning resources into smaller units.

For example, cookies wrapped individually, a household budget divided into categories (e.g. rent, food, utilities, transportation etc.).

When a resource is divided into smaller units, consumers encounter additional decision points – a psychological hurdle encouraging them to stop and think.

Peak-End Rule

People judge an experience largely based on how they felt at its peak (the most intense point) and its end, rather than on the total sum or average of every moment of the experience.

The effect occurs regardless of whether the experience is pleasant or unpleasant and how long the experience lasted.

In a research, participants engaged with two experiences: short and long trial.
In the short trial, they soaked their hands in water at 14 C for 60s.
In the long trial, the same participants soaked their hands in water at 14 C for 60s and kept their hands under the water for extra 30s at 15 C.
When the researchers asked the participants to choose which trial to repeat, the majority chose the long trial.

Similarity, a study showed that in uncomfortable colonoscopy procedures, patients evaluated the discomfort of the experience based on the pain at the worst peak and the final ending moments. This occurred regardless of the procedure length or the pain intensity.


When people are exposed to one stimulus, it affects how they respond to another stimulus.

Their unconscious brain is affected by stimulus like colors, words or smells, which created an emotion that will affect their next actions.

For example, one study revealed that when restaurants played French music, diners ordered more wine.

In a different study, when websites’ visitors were exposed to a green background with pennies on it, they looked at the price information longer than other visitors.


The avoidance of doing a task that needs to be accomplished.

It is the practice of doing more pleasurable things in place of less pleasurable ones or carrying out less urgent tasks instead of more urgent ones.

It is estimated that 90% of college students engage in procrastination, and 75% consider themselves procrastinators.

Projection Bias

The tendency of people to overestimate the degree to which other people agree with them. People tend to assume that others think, feel, believe, and behave much like they do.

This bias also influences people’s assumptions of their future selves. They tend to believe that they will think, feel, and act the same in the future as they do now.

For this reason, we sometimes make decisions that satisfy current desires, instead of pursuing things that will serve our long-term goals.

For example, if people go to the supermarket when they are hungry – they tend to buy things they don’t normally eat and spend more money as a result. This happens because at the time of shopping they unconsciously anticipate that their future hunger will be great as it is now.

Ratio bias

People’s difficulties in dealing with proportions or ratios as opposed to absolute numbers.

In a study, participants rated cancer as riskier when it was described as killing 1,286 out of 10,000 people than as killing 24.14 out of 100 people. The fact that 12.86% could be considered riskier than 24.14% is a clear demonstration that the ratio bias can strongly influence the perception of risk.

In a similar study, participants rated the statement “36,500 people die from cancer every year” as riskier than the statement “100 people die from cancer every day”.


If someone does something for you, you’ll naturally want to do something for them.

When you offer something for free, people feel a sense of indebtedness towards you.

For example, researchers tested how reciprocity can increase restaurant tipping. Tips went up to 3% when diners were given an after-dinner mint. Tips went up to 20% if, while delivering the mint, the waiter paused, looked the customers in the eye, and then gave them a second mint while telling them the mint was especially for them.

In another study, 11% of people were willing to donate an amount worth one day’s salary when they were given a small gift of candy while being asked for a donation, compared to 5% of those that were just asked for the donation.

Regret aversion

People anticipate regret if they made a wrong choice, and take this anticipation into consideration when making new decisions. Fear of regret can play a large role in dissuading or motivating someone to do something.

For example, an investor decides to buy a stock based on a friend’s recommendation. After a while, the stock falls by 50% and the investor sells the stock at lost.
To avoid this regret in the future, the investor will research any stocks that his friend recommends.

On the other hand, if the investor didn’t take his friend recommendation and the price increased by 50%, next time the investor would be less risk averse and would buy any stocks his friend recommends.

Representativeness heuristic

People tend to judge the probability of an event by finding a ‘comparable known’ event and assuming that the probabilities will be similar.

When people rely on representativeness to make judgments, they are likely to judge wrongly because the fact that something is more representative does not actually make it more likely.

For example, in series of 10 coin tosses, most people judge the series HTHTTTHHTH to be more likely than the series HHHHHHHHHH.

In business, if a customer meets a salesman from a certain company that is aggressive, the customer might assume that the company has an aggressive culture.

In finance, investors might prefer to buy a stock based on the company’s positive characteristics (e.g. high-quality products) as an indicator for a good investment.


The more difficult it is to acquire an item the more value that item has.

When there is only a limited number of items available. The rarer the opportunity, the more valuable it is.

People assume that things that are difficult to obtain are usually better than those that are easily available. They link availability to quality.

On “Black Friday”, more than getting a bargain on a hot item, shoppers thrive on the competition itself, in obtaining the scarce product.

In a famous study, one group of participants were given a jar with ten cookies, a second group was given two cookies, and a third group was initially given ten cookies, which were then reduced to two cookies. when asked the participants to rate their cookies, the third group rated their cookies the highest.

Social proof

A psychological phenomenon where people reference the behavior of others to guide their own behavior.

Studies show that over 70% of Americans say they look at product reviews before making a purchase and 83% of consumers say they trust recommendations over any other form of advertising.

There are five types of social proof for your product or service:

  1. Experts social proof – an approval from credible industry leaders.
    If people buy something that they’re unfamiliar with, they tend to rely on expert’s opinion.
  2. Celebrity social proof – an approval or an endorsement from celebrities.
    Celebrities are walking advertisements, so any product or service that they recommend or are seen using are bound to get a lot more attention.
  3. User social proof – an approval from current customers/users of a product or service.
    This includes customer testimonials, case studies, and product/service reviews.
  4. Wisdom of the crowd – an approval from a large group of people.
    When lots of people are using or buying a product, others want to follow.
  5. Wisdom of friends – an approval from friends and people you know.
    92% of consumers trust recommendations from people they know and pay 2X more attention to recommendations from friends.

Sunk Cost Fallacy

The tendency of people to irrationally follow through on an activity that is not meeting their expectations because of the time and/or money they have already spent on it.

The logic form:
X has already been invested in project Y.
Z more investment would be needed to complete project Y, otherwise X will be lost.
Therefore, Z is justified.

The sunk cost fallacy explains why people finish movies they aren’t enjoying, finish meals in restaurants even though they are full, hold on to investments that are underperforming and keep clothes in their closet that they’ve never worn.

Zero Price Effect

When any item priced at exactly zero will not only be perceived to have a lower cost but will also be attributed greater perceived value.

When people are offered something for free, they have an extremely positive reaction that clouds their judgment.

In an experiment, one group of participants were given three choices: Buy a “low-value product” (a Hershey’s Kiss) for one cent, buy a “high-value product” (a Lindt truffle) for 14 cents, or buy nothing. The second group faced a slightly different choice, in which the cost of each chocolate was lowered by a single cent. The Lindt truffle was now 13 cents, while the Hershey’s Kiss was free.

The results showed that when both chocolates are not free, the majority preferred the higher value product. But when the lower value product was offered free, the majority of people preferred it.

Stolen from here!

And then there’s this massive list!