What is Thinking, Fast and Slow about, in plain words?

Daniel Kahneman was a psychologist whose research on judgement and decision-making, much of it with Amos Tversky, led to prospect theory, the work behind his Nobel Prize. Thinking, Fast and Slow, published by Farrar, Straus and Giroux in 2011, is his summing-up of that life's work for a general reader. It became a bestseller, sold more than a million copies within about a year, and won the National Academy of Sciences Best Book Award in 2012.

The two systems, in plain words

• System 1 is the fast mind: automatic, emotional and largely unconscious. Think of the instant impression you form of a stranger, or the answer to two plus two arriving before you ask for it.
• System 2 is the slow mind: effortful, logical and conscious. Think of comparing two mortgage offers line by line, or checking an argument for holes.

They are best understood as two ways of forming thoughts rather than two places in your head. The central point is that System 1 runs most of the show, and System 2, which we think of as "us", often just endorses what System 1 has already decided.

The biases readers remember

• Anchoring. An irrelevant number influences your estimate. Hear a high number first, and your guess drifts upward.
• Availability. Things that come easily to mind, because they are vivid or recent, seem more common than they are.
• WYSIATI: what you see is all there is. We build confident stories from the information in front of us and ignore what we do not know.
• The planning fallacy. We underestimate how long and how much things will cost. Anyone who has renovated a kitchen knows this chapter by heart.
• Loss aversion. Losing something hurts more than gaining the same thing pleases.
• Framing. The same facts, presented differently, lead to different choices. A treatment with a 90 per cent survival rate sounds better than one with a 10 per cent mortality rate, though they are identical.
• Sunk costs. We keep investing in failing projects because stopping would mean admitting the loss.

The two selves

Late in the book, Kahneman distinguishes the experiencing self, which lives through each moment, from the remembering self, which tells the story afterwards. The remembering self judges experiences mostly by their peak and their ending, not their length. It is a strangely useful idea for planning anything from a holiday to a dinner party: the ending matters more than you would think.

The caveats

The book is now read with an asterisk. Several studies on priming cited in an early chapter failed to replicate during psychology's replication crisis, and Kahneman himself acknowledged that he had placed too much faith in underpowered studies. One later analysis went further and argued that much of the book rests on research with shaky foundations. Read it as a brilliant framework, not as a list of settled facts.

Which parts to read first

The book is long, and few people read every page. A sensible route:

1. Part 1, Two Systems. The foundation. Read it all.
2. Part 2, Heuristics and Biases. The famous chapters on anchoring, availability and the Linda problem.
3. Part 4, Choices. Prospect theory, loss aversion and framing, the heart of his Nobel work.
4. Part 5, Two Selves. Short and memorable.
5. Part 3, Overconfidence. Excellent, especially on hindsight and expert prediction; read it once the rest has won you over.

Skim where it gets technical. You will still get most of the value.