Kahneman quietly rewired the way most of the world thinks about thinking — and he won a Nobel Prize in Economics for it, despite being a psychologist, because economics had to acknowledge humans don't behave the way economists assumed.
His big idea, with his collaborator Amos Tversky: you don't have one mind. You have two. System 1 is fast — pattern-matching, intuition, gut reaction. System 2 is slow — reasoning, weighing, doing math. System 1 runs almost everything. System 2 is lazy and rarely shows up.
The catch: System 1 is wired for shortcuts, and the shortcuts have systematic blind spots. Loss aversion (losing $100 hurts more than winning $100 feels good). Anchoring (the first number you hear shapes every estimate after). Availability (you fear what you can picture, not what's actually likely). Dozens of these. Most decisions you think you 'made' came pre-cooked by biases you didn't notice.
His book Thinking, Fast and Slow walks through it without making you feel stupid. Read it and you'll catch yourself in your own biases in real time. Which is exactly his point — you can't shut System 1 off, but knowing it's there is half the fight.
He died in 2024. Long career, real intellectual humility, and probably more useful to anyone trying to think clearly than almost any self-help book on the shelf.