Thinking, Fast and Slow

I found it tedious and long to get through. But I can still appreciate it for what it is. It just wasn't for me. Yet I still think that the core content, had it been in shorter book, would have interested me very much. It's a great psychology book. Probably one of the best. But I wasn't interested in all the technical details that this book had to offer, hence the low rating. Still, the core concepts are very interesting and gives great insight into how our mind works.

6 min read

Two Systems

The Characters of the Story

System 1 operates automatically and quickly, with little or no effort and no sense of voluntary control.

System 2 allocates attention to the effortful mental activities that demand it, including complex computations (//math, for example). The operations of System 2 areoften associated with the subjective experience of agency, choice and concentration.

From what I've read so far, it seems that it can be boiled down to: System 1 is what you immediately think of, without any mental steps. System 2 are what takes time to process, and which you actively have to think about.

For example, a System 1 thing would be to immediately give the answer to 2 + 2 = ?. But also something like detecting hostility in a voice.

If you are sufficiently proficient at something, you might even be able to come up with great solutions to a given problem. For example, a Chess master would immediately find a strong move in a given situation, but a beginner would have to think long and hard about it.

The highly diverse operations of System 2 have one feature in common: they require attention and are disrupted when attention is drawn away.

For example to search your memory to identify a surprising sound, or to focus on the voice of a particular person in a crowded and noisy room. Both tasks are disrupted when your attention is drawn away.

The often-used phrase "pay attention" is apt: you dispose of a limited budget of attention that you can allocate to activities, and if you try to go beyond your budget, you will fail. It is the ark of effortful activities that they interfere with each other, which is why it is difficult or impossible to conduct several at once. You could not compute the product of 16 x 24 while making a left turn into dense traffic - and you should certainly not try.

You can do several things at once, but only if they are easy and undemanding. Say, talking to someone while driving on an empty highway.

System 1 and System 2 are always active when we are awake. System 1 runs automatically, and System 2 is normally in a comfortable low-effort mode, in which only a fraction of its capacity is engaged.

System 1 gives suggestions to System 2, which it can act upon or give attention.

A limitation of System 1 is that it cannot be turned off. If you are shown a word on the screen in a language you know, you will read it - unless your attention is totally focused elsewhere.

One of the tasks of System 2 is to overcome the impulses of System 1. In other words, System 2 is in charge of self-control.

Learn to recognize situations in which mistakes are likely and try harder to avoid significant mistakes when the stakes are high.

System 1 and System 2 are not systems in the standard sense of entities with interacting aspects or parts. And there is no one part of the brain that either of the systems would call home. They are only there to improve the understanding for the reader. System 1 and System 2 are simply nicknames, and could be called anything else.

Attention and Effort

The pupil is a good measure of the physical arousal that accompanies mental effort.

The pupils increase in size when the testee is exerting heavy mental effort. Likewise they shrink when the testee gives up or finishes the task.

Highly intelligent individuals need less effort to solve the same problems, as indicated by both pupil size and brain activity.

The Lazy Controller

One of the main functions of System 2 is to monitor and control suggestions from System 1, however it is often lazy and places too much faith in intuition.

The Associative Machine

Cognition is embodied; you think with your body, not only with your brain.

Priming: If shown the word WASH, you'd be much more likely to fill SO_P as SOAP instead of SOUP. Likewise, you'd be more likely to fill it as SOUP, had you been shown the word EAT.

Reciprocal priming effects tend to produce a coherent reaction: if you were primed to think of old age, you would tend to act old, and acting old would reinforce the thought of old age.

Cognitive Ease

A reliable way to make people believe in falsehoods is frequent repetition because familiarity is not easily distinguished from truth.

You act differently when experiencing cognitive ease vs. strain; you’ll probably make less errors when strained, but you won’t be as creative.

Norms, Surprises, and Causes

The main function of System 1 is to maintain and update a model of your personal world, which represents what is normal in it.

A Machine for Jumping to Conclusions

System 1 is radically insensitive to both the quality and the quantity of the information that gives rise to impressions and intuitions.

How Judgements Happen

When making judgements, we often either compute much more information than we need, or we attempt to match the underlying scale of intensity across dimensions.

Answering an Easier Question

If a satisfactory answer to a hard question is not found quickly, System 1 will find a related question that is easier and answer it instead.

The Law of Small Numbers

The law of small numbers is part of two larger stories about the workings of the mind.

  • The exaggerated faith in small samples is only one example of a more general illusion - we pay more attention to the content of messages than to information about their reliability, and as a result end up with a view of the world around us that is simpler and more coherent than the data justify. Jumping to conclusions is a safer sport in the world of our imagination than it is in reality.
  • Statistics produce many observations that appear to beg for casual explanations but do not lend themselves to such explanations. Many facts of the world are due to chance, including accidents of sampling. Casual explanations of chance events are inevitably wrong.

We have a strong bias towards believing that small samples closely resemble the population from which they are drawn.


The anchoring effect occurs when a particular value for an unknown quantity influences your estimate of that quantity.

Anchoring effect: When people consider a particular value for an unknown quantity before estimating that quantity. The estimates stay close to the number that people considered.

There is a form of anchoring that occurs in a deliberate process of adjustment, an operation of System 2. And there is anchoring that occurs by a priming effect, an automatic manifestation of System 1.

Anchoring as adjustment

Start from an anchoring number, assess whether it is too high or too low, and gradually adjust your estimate by mentally "moving" from the anchor. This process typically ends prematurely, because people stop when they are no longer certain that they should move farther.

Insufficient adjustment neatly explains why you are likely to drive too fast when you come off the highway onto city streets - especially if you are talking with someone as you drive.

People who are instructed to shake their head when they hear the anchor, as if they rejected it, move farther from the anchor, and people who nod their head show enhanced anchoring. Adjustment is also an effortful operation. People adjust less when their mental resources are depleted, either because their memory is loaded with digits or because they are slightly drunk. Insufficient adjustment is a failure of a weak or lazy System 2.

Anchoring as Priming Effect

A process that resembles suggestion is indeed at work in many situations: System 1 tries its best to construct a world in which the anchor is the true number.

Uses and Abuses of Anchors

Daniel gave some advice to students when he taught negotiations: if you think the other side has made an outrageous proposal, you should not come back with an equally outrageous counteroffer, creating a gap that will be difficult to bridge in further negotiations. Instead you should make a scene, strom out or threaten to do so, and make it clear - to yourself as well as to the other side - that you will not continue the negotiations with that number on the table.

In general, a strategy of deliberately "thinking the opposite" may be a good defense against anchoring effects, because it negates the biased recruitment of thoughts that produces these effects.

The Science of Availability

The ease with which we can think of examples is often used to judge the frequency of events.

Availability, Emotion, and Risk

We try to simplify our lives by creating a world that is much tidier than reality; in the real world, we often face painful tradeoffs between benefits and costs.

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