Last reviewed: 20 October 2026

Richard Feynman

1918–1988

American physicist, Nobel laureate and famous explainer of science.

What they got right

He made honesty with yourself the first rule: actively look for the ways you might be fooling yourself before you fool anyone else.

Skill it shows

Cognitive biases

Practise this skill

The first principle is that you must not fool yourself—and you are the easiest person to fool.

'Cargo Cult Science', Caltech commencement address (1974), Engineering and Science, June 1974 Source

Worth knowing

His own accounts describe behaviour toward women that is widely criticised today. Many quotes credited to him online are misattributed.

Try it yourself

Recall a time you were sure you were right and turned out wrong. What made you so easy to fool?

More about Richard Feynman

Richard Feynman was an American theoretical physicist, born in 1918, died in 1988, and a Nobel laureate for work on quantum electrodynamics. He is in this group because his warnings about self-deception became part of how people talk about thinking, not because he wrote a system of philosophy. The 1974 Caltech commencement address, published as 'Cargo Cult Science', states the first principle he wanted young researchers to keep: do not fool yourself. The Character of Physical Law, the 1965 Messenger Lectures, says what happens when a guess disagrees with experiment. What Do You Care What Other People Think? tells his father's lesson that the name of a bird is not knowledge of the bird. A line on his office blackboard is his, and it is a note, not a paper. Sentences that merely sound blunt and American are not therefore his.

Do not fool yourself
The first safeguard in the 1974 address. Other people are easier to deal with once you have stopped lying to yourself.
Experiment decides
A beautiful guess that disagrees with experiment is wrong. The method is guess, compute, compare.
Names are not knowledge
Knowing what a thing is called, in any number of languages, is not the same as knowing what it does.