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# Thinking, Fast and Slow: Part 1, Chapter 2 Summary & Analysis

Summary
Analysis
In chapter 2, Kahneman advises readers to try an exercise: write out several strings of four digits, and, while keeping a steady beat, report each string, wait two beats, and then report the same string but add one to each digit. So, for example, if the string is 5294, a person should read out that number, and then say aloud 6305. Most people have a difficult time with this exercise.
Kahneman’s exercises continue to raise our awareness of the limits of our attention and mental effort. We can focus our System 2 on calculations, but it is difficult to do this at the same time as another process: keeping a beat. Our laziness leads us to want to focus on one or the other.
Themes
In experiments, Kahneman and a colleague—Jackson Beatty—found that people’s eyes dilated the harder they worked during this exercise. People’s eyes dilated most when they were asked to add three to each digit; with anything more demanding, people simply gave up. This also led Kahneman to observe that in casual conversation, people’s eyes did not dilate at all. Mental life is normally conducted without much effort.
The giving up described in this exercise is distinct from the laziness people exhibit for other problems; in examples that Kahneman will describe in later chapters, our minds simply tend towards exerting as little effort as possible. This is not the same, however, as being asked to exert mental effort beyond our capacity.
Themes
The Add-3 exercise also reveals that we cannot expend more energy on a mental task than we need. One would never be able to spend more energy memorizing four digits than in completing the Add-3 exercise, because we simply do not need as much energy to do so, and will always use the least amount of energy possible.
The fact that we cannot extend more energy than a task requires likely led to our tendency towards laziness: even when we are able to exert additional necessary energy for a task, we often forgo that effort.
Themes
Additionally, as a person becomes skilled in a task, its demand for energy diminishes. Talent has similar effects. Highly intelligent individuals need less effort to solve the same problems, which we know both from monitoring both pupil size and brain activity.
Although intelligence may allow people to expend less effort, they are only slightly less immune to certain fallacies—proving that even intelligent people can still be lazy thinkers.
Themes
Kahneman then questions what makes certain tasks more demanding than others. He believes that more effort is required to maintain several ideas that require separate actions, or in which information has to be combined to make decisions—like choosing between two options at a restaurant. Time pressure, as experienced in Add-3, is another driver of effort.
Time pressure is likely a big driver of effort because, as Kahneman goes on to explain in chapter 3, we not only expend effort in whatever calculations we must make,  but we must also spend effort in order to force ourselves to focus.
Themes
Switching between tasks is also difficult, because we train our brains to accomplish a particular task when we focus on it. For example, if we are asked to count all the instances of the letter f on a page, it would not come naturally, but gradually we would train ourselves to focus on the letter f. But if we were then asked to count the commas in a page, we would have to overcome our newly acquired tendency to focus on the letter f.
This point relates to some of Kahneman’s later explorations of expertise. Experts (like chess masters) are able to learn and recognize patterns in their area of expertise, and therefore they do not need to expend as much energy making various calculations and assumptions. When we train our brains to learn something specific, we are building up our expertise.
Themes
Kahneman finishes the chapter by commenting that very few things in our lives force us to expend as much mental effort as Add-3. We avoid mental overload by breaking up work into easy steps, or by relieving our working memory when we use pencil and paper rather than trying to hold a variety of information in our head. We take our time and try to expend as little energy as possible.
When we encounter situations that require a significant amount of mental effort, we work to avoid our laziness through strategies like the ones that Kahneman mentions here. But there are some incorrect calculations that we make without much mental effort; and we have a difficult time overcoming these biases because we are too lazy to check our work.
Themes