Thinking, Fast and Slow Summary

One Paragraph Summary By reading the book, we will get a better understanding of the human mind. The author shows us how we make decisions and how we can improve our decision-making in the future. If you want to learn how your brain works, how to solve problems better, and how to judge situations better, you should read this brilliant book.

Thinking, Fast and Slow Summary

Thinking, Fast and Slow—Intuition or deliberation? Where you can (and can't) trust your brain
A book by Daniel Kahneman

By writing the Thinking, fast and slow Summary I learned the following three things:

  • Laziness is built deep into our nature
  • Wording and repetition influences our decision-making
  • It will be easier to make better decisions in the future

Key Ideas

We have two minds, one is automatic, and the other is considered

You can think of yourself as not being one character, but two. The first character is impulsive, intuitive, and acts on auto-pilot. The second character is thoughtful, deliberate, and calculating. Those two characters are in a constant struggle. Those two characters determine how we, as a person, make our decision and act in the world.

The first character always acts fast without deep thinking.

When you hear a loud bang and startle, it was the first character's turn.

When you do deep thinking, such as deciding which choice to make or solving a math problem with your full focus and attention, character two is in control.

For example, if you try to find your wife within a crowd of people. You will try to remember what she is wearing. To find your wife, you will need your fullest attention and focus. This effort, with the most thorough care, is something character two would do.

Those two characters determine our judgments, decisions, and behavior, day in and out.

Question: A bat and a ball cost together 1.10 dollars. The bat costs one dollar more than the ball. How much does the ball cost?

If your answer is 10 cents, then your system one thinking is responsible for the reply. You wanted to trust your intuition and gave control to character one. The good thing is your answer was fast. The problem, though, is that the answer is wrong.

When you answered that the ball costs 5 cents, you probably gave the task of finding a solution to character two. Character two focused his full attention on solving the problem. It took him a little longer than character one, but he gave the correct result: 5 cents.

Most people provide the wrong answer. Why? When we are faced with a problem, we usually want to find a quick solution. The bat and ball problem seems so simple that most of us let character one solve it. But we should have called upon character two instead because the bat and ball problem is a more complicated question than we initially anticipated.

If you want to increase your intelligence score, you should put character two more often in control.

Our thoughts and actions are often on autopilot

Here is a word fragment SO_P?

What do you think? Nothing? Here is a second word, EAT. What do you think now when you look at the word fragment again? Probably you fill in the space with the character U:

When you were given the word SHOWER as the second word and would have looked at the word fragment again, you probably would have filled in the character A for soap.

Filling missing information relying on the context is known as priming.

Priming affects our thinking and the way we act. For example: when you are on a walk through a park and are primed with words associated with being elderly, you will find yourself walking slower than usual.

The frightening thing is that this priming of your thinking and behavior is unconscious. We do not know that we are affected by priming.

This means that you are seldom in conscious control of your actions and thinking. There are always things in our environment that do influence us.

Priming and cognitive biases

Do you know what exaggerated emotional coherence is?

Suppose you meet somebody called Ben at a party and he is amiable. Later someone else will ask you if you know somebody who would like to contribute to a charity. You instantly would think of Ben.

Because Ben was so friendly to you and your brain tends to oversimplify information, you recommend Ben. You put a halo on Ben.

Therefore this effect is also known as the halo effect.

There are other scenarios where our brains oversimplify things. For example, there is a cognitive bias called confirmation bias.

Confirmation bias is the tendency to agree with the information that confirms your current world view.

But why do we fall into those traps? Well, our brains love to make quick decisions without the need to invest too much energy. It is faster to fill in missing information than to use our fullest attention to find and evaluate the missing data.

Priming and cognitive biases affect our judgments, actions, and choices immensely.

Humans love making quick decisions

Many situations demand us to come up with a quick answer. Humans use heuristics to be able to make these quick decisions.

Take the substitution heuristic as an example. Using this heuristic means to substitute a complicated question with one that we can answer more quickly.

This is the essence of intuitive heuristics: when faced with a difficult question, we often answer an easier one instead, usually without noticing the substitution.―Daniel Kahneman

Consider the question if a person can do a specific job. Because we have not enough information about that person and what experience that person has to do the job well, we replace the questions with Does this person look like someone who will do this job well?. To answer these questions, we merely need to ask if that person looks like someone who can do the job. We do not need to do the thorough research required for a rational decision.

The base rate is your friend when you need to make predictions

If you want to make better predictions, you should base your decisions on data and not so much on what you expect. To do this, we should always find the base rate and make our predictions using it.

It is widespread that people neglect the base rate when they need to make predictions.

We should also remember that every variation from the average will eventually regress to the average.

For example, if you order a cab and you know that the cab company has 20 yellow cabs and 80 red cabs. It is quite easy to make a prediction. The taxi that will pick you up will probably be a red cab even if you have been picked up by a yellow cab the last ten times.

Cognitive ease and cognitive strain

Our brains can be in two states. The first is the state of cognitive ease, and the second is the state of cognitive strain.

Your mind is in cognitive ease when the task at hand does not need our fullest attention. In this state, our brain only consumes little energy.

On the other hand, if the task needs our focused attention, we enter the state of cognitive strain and consume lots of energy.

When we are in a state of cognitive ease, we are more intuitive, creative, and happier. But we are also more likely to make mistakes.

In the state of cognitive strain, we use more energy as we double-check our decisions to avoid making errors. The disadvantage is that we are less creative in this state.

The wording of probabilities influences your decision making

A probability can be expressed as a relative frequency or as a statistical probability.

For example, if we say 10 out of 100 persons, we express the probability as a relative frequency.

On the other hand, we can express the same probability as a statistical probability: 10 percent.

Interestingly if we need to make a judgment based on the same numbers, but these numbers get expressed differently, it will influence our decision immensely.

In the Mister Jones experiment, this effect has been proofed. Two groups of psychiatric professionals were asked if it was safe to release Mr. Jones from the psychiatric clinic. In the first group, the probability that Mr. Jones would commit a crime after his release was expressed as being 10 percent (statistic probability) likely. The second group received the same data in different wording. They told the professional that from 100 patients like Mr. Jones, ten would commit a crime after being released from the hospital. Twice as many professionals in the second group denied the discharge of Mr. Jones.

We do not see utility as rational as utility theory thinks

Imagine two people having both 5 million dollars. Utility theory would argue that they should be both equally happy because the 5 million dollars gives both of them the same utility.

Now we learn that both persons went to the casino before having those 5 million dollars. The first person entered the casino with 1000 dollars and left it with 5 million. The second person came to the casino with 8 million dollars and lost 3 million. Both persons had the same amount of money when they left the casino. It becomes evident that both persons will not be equally happy.

To some degree, utility theory must be flawed.

Kahneman is challenging utility theory with an alternative, the prospect theory. Prospect theory tries to explain why our choices are not always rational.

One explanation is that we fear losses more than we value gains. This phenomenon is called loss aversion.

First Insight: Laziness is built deep into our nature

A general law of least effort applies to cognitive as well as physical exertion. The law asserts that if there are several ways of achieving the same goal, people will eventually gravitate to the least demanding course of action. In the economy of action, effort is a cost, and the acquisition of skill is driven by the balance of benefits and costs. Laziness is built deep into our nature.―Daniel Kahneman

When I think about laziness from an evolutionary standpoint, it is quite evident that being lazy is a competitive advantage. When you can live with fewer resources, you will have a better chance to survive.

This evolutionary advantage might be the reason we tend to be in a low power consumption mode, like our laptops. Only when we need to focus our attention and double-check decisions, we will leave the low power consumption mode. When we have completed the calculation, it makes sense to switch back to the energy-saving mode immediately.

If we are aware that laziness is our default mode, we can make deliberate decisions to switch.

Second Insight: Wording and repetition influences our decision-making

The wording of the information we are trying to process is essential. As wording is priming us unconsciously and might have a significant impact on the outcome. Like the wording, the environment can influence us as well. We are different persons when we are in a crowd of colleagues than when we are alone. If you make a decision in a group of observers, it might be a different decision than the one you would have made being alone.

A reliable way of making people believe in falsehoods is frequent repetition, because familiarity is not easily distinguished from truth.―Daniel Kahneman

I knew this before, but it is good to get a reminder. The more often you read or hear something, the more likely will you accept the message as being correct. Marketers and politicians are well aware of this and use this technique all the time to influence us.

Third Insight: It will be easier to make better decisions in the future

We can be blind to the obvious, and we are also blind to our blindness.―Daniel Kahneman

With all the great insights Kahneman delivers, it will be easier to make a better decision in the future. It will not be easy, just easier than before.

I think the first thing we need to do to be able to make better decisions in the future is to know what traps we can fall into. And Thinking, Fast and Slow lets us see some traps we didn't see before.

It is a good thing to know about our default mode of thinking and all the cognitive biases that we have.


There are two characters in our mind that continuously struggle to make decisions for us. Becoming aware of this struggle will help us in the future to make better judgments and decisions.

The premise of this book is that it is easier to recognize other people's mistakes than our own.―Daniel Kahneman

The book will also show us how often we come to conclusions to fast. With this insight, we will be better friends, partners, colleagues, and humans.


  • Avoid laziness in thinking to avoid errors
  • If you want to give better answers use your focused attention more often
  • Be aware of what priming is
  • Be mindful that our environment is full of things influencing our decisions and our behavior
  • Be aware that the mind makes quick decisions even when lacking information
  • Be mindful of the halo effect to avoid too quick judgments
  • Be aware of cognitive biases that influence your thinking immensely
  • Keep the base rate in mind when making decisions
  • Do not make decisions on what you expect, base decisions on data
  • Remember that everything regresses to the mean
  • Try to relax when you want to be creative
  • Don't let rare statistical events influence your decision-making
  • Make your messages more persuasive by repeating them
  • Look closely at the wording of probabilities when you need to make decisions

Thinking, Fast and Slow Summary—related resources

  Read more about Daniel Kahneman on Wikipedia.

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If you liked reading the Thinking, Fast and Slow Summary, you should also read You Are Not Listening Summary.

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