Cross posted from my personal blog. In this post, I'm going to assume you've come across the Cognitive Reflection Test before and know the answers. If you haven't, it's only three quick questions, go and do it now. One of the striking early examples in Kahneman's Thinking, Fast and Slow is the following problem: > (1) A bat and a ball cost $1.10 in total. The bat costs $1.00 more than the ball. > How much does the ball cost? _____ cents This question first turns up informally in a paper by Kahneman and Frederick, who find that most people get it wrong: > Almost everyone we ask reports an initial tendency to answer “10 cents” because the sum $1.10 separates naturally into $1 and 10 cents, and 10 cents is about the right magnitude. Many people yield to this immediate impulse. The surprisingly high rate of errors in this easy problem illustrates how lightly System 2 monitors the output of System 1: people are not accustomed to thinking hard, and are often content to trust a plausible judgment that quickly comes to mind. In Thinking Fast and Slow, the bat and ball problem is used as an introduction to the major theme of the book: the distinction between fluent, spontaneous, fast 'System 1' mental processes, and effortful, reflective and slow 'System 2' ones. The explicit moral is that we are too willing to lean on System 1, and this gets us into trouble: > The bat-and-ball problem is our first encounter with an observation that will be a recurrent theme of this book: many people are overconfident, prone to place too much faith in their intuitions. They apparently find cognitive effort at least mildly unpleasant and avoid it as much as possible. This story is very compelling in the case of the bat and ball problem. I got this problem wrong myself when I first saw it, and still find the intuitive-but-wrong answer very plausible looking. I have to consciously remind myself to apply some extra effort and get the correct answer. However, this becomes more complicat