His book has sold a million copies in the UK, yet Daniel Kahneman tells 2,000 fans packed into Central Hall Westminster that he had a miserable time writing it. The question he is asking us and himself is why did his book sell so well?

A winner of the Noble Prize for Economics, Kahneman explains that he is a psychologist and not an economist. His bestseller, Thinking, Fast and Slow, is 400 pages of brilliantly explained ideas and subtle brain teasers that demonstrate how our minds work.

[pull_quote_right]Part of what it means to be you is that your thoughts, beliefs and actions are not generated as much by reason as you think[/pull_quote_right]

The first 100 pages deal with the key theme that the human mind has two parts: System One (thinking fast) and System Two (thinking slow).

“I set out to document the split of the mind between reason and passion,” he says. Reason is the word of System Two thinking, like answering a question such as ‘What is 17 times 24?’ It is effortful thinking and you need a pen and paper.

Two is the part of our brain that seeks to control our actions and to inhibit our impulses. When we stop ourselves from telling someone to go to Hell, that is Two at work.

Two likes to generate stories to explain our beliefs. We feel that we have to have a reason for doing things. This storytelling instinct is innate, he says.

A purpose of his book, he says, is that most of what happens in our mind happens automatically. We are not conscious of constructing the scenes that we look at.

One continuously interprets the world for us without us having to think. Kahneman stresses that he does not argue that either is the superior system. System One is very effective, he says. “When we enter into a room, we get a sense of whether people like us. It is usually accurate and it just happens,” he says.

However, One sometimes produces odd results. Kahneman tells a story of being out to dinner with his wife and another couple. Afterwards his wife tells him that the other man is sexy. Kahneman is surprised by this. But even more so when she says: “He does not undress the maid himself.” Perplexed, he asks his wife what she means and she repeats herself. This time he listens closely. “He does not underestimate himself,” she says.

Or consider this question: A bat and ball cost £1.10. If the bat costs £1 more than the ball, how much does the ball cost? Most people get this wrong. At Harvard the brightest students in America score about 50%. At other universities they do worse. The reason for the difference? Most people don’t check their answers. System Two simply trusts System One to get the answer right.

Kahneman says Two doesn’t control what One does but instead endorses One. Part of the story of what it means to be you is that your thoughts, beliefs and actions are not generated as much by reason as you think.

The causes of our political beliefs are not rational but because we believe in people who tell us things, people who we love. Most of our successes come from System One. One knows the answer and produces it.

However, One is not dumbfounded when it does not know the answer. It makes an answer up and always according to
its own rules. We are rationally irrational.

Kahneman says the human mind is basically reasonable, if not reasoned. Reading his book will make you wiser, perhaps richer and no less prone to error.