He finishes by explaining he has demonstrated three main tensions in the book - two characters, two species, and two selves.
The two characters were the intuitive System 1, which does the fast thinking, and the effortful and slower System 2, which does the slow thinking, monitors System 1, and maintains control as best it can within its limited resources. The two species were the fictitious Econs, who live in the land of theory, and the Humans, who act in the real world. The two selves are the experiencing self, which does the living, and the remembering self, which keeps score and makes the choices.
So he demonstrates how the "fast" and subconscious System 1 often jumps to conclusions or uses whatever evidence is immediately to hand, and the "slow" deliberate System 2 is often too lazy to overrule it.
System 1 - the fast, subconscious thought which is always turned on - also likes to substitute easier questions for harder ones, which it then answers with self-confident gusto.
This is the essence of intuitive heuristics: when faced with a difficult question, we often answer an easier one instead, usually without noticing the substitution.This isn't a matter of simplifying into a parsimonious model, either. We typically don't even notice if our immediate intuitive mind has decided to jump to a conclusion. Remembering reference classes, checklists and slower, more methodical decision-making can help - a little.
He shows the homo economicus model of traditional economics is empirically without foundation. Indeed, humans cannot be rational in many situations. If rationality is making consistent choices, we typically fail to do so if the choices are framed differently. The self which experiences life at the time is also different from the self which remembers experience. The remembering self does not realy think about duration of an experience, but only the peak feeling and the end-point.
The central fact of our existence is that time is the ultimate finite resource, but the remembering self ignores that reality. The neglect of duration combined with the peak-end rule causes a bias that favors a short period of intense joy over a long period of moderate happiness.
All the ways you can go wrongFrankly, the book makes you feel queasy, because even if you know the pitfalls it is still difficult to avoid making mistakes. He has multiple examples of experts stumbling on their own expertise, and basic errors in consistency and judgment. Kahneman himself says he still falls into many of the traps. But he hopes a vocabulary to talk about the kind of mistakes people make, including the increasingly familiar terms like availability heuristic or prospect theory. If nothing else, it is a checklist to avoid making some errors - although he laments that psychology students typically do not learn to apply what they learn in the classroom to their decisions outside it.
It is an argument above all for a certain humility about our abilities.
A recurrent theme of this book is that luck plays a large role in every story of success; it is almost always easy to identify a small change in the story that would have turned a remarkable achievement into a mediocre outcome. Our story was no exception.