Feynman quotes, checked

Feynman is one of the most quoted scientists there is, and plenty of the lines credited to him are things he never said. Each page below takes one popular quote back to its original source: the book and page, the lecture, the report. So far we have checked 5 quotes: 1 misattributed, 1 paraphrased, 3 real.

• Misattributed “Shut up and calculate!” Misattributed. Nobody has found a source in which Feynman says it. The earliest known use is a 1989 column by physicist N. David Mermin.
• Paraphrased “If you think you understand quantum mechanics, you don’t understand quantum mechanics.” Paraphrased. The popular version isn’t in his books. What he said was “I think I can safely say that nobody understands quantum mechanics.”
• Real “For a successful technology, reality must take precedence over public relations, for nature cannot be fooled.” Real, word for word. It’s the closing sentence of Feynman’s appendix to the presidential commission’s report on the Challenger accident (1986).
• Real “Science is the belief in the ignorance of experts.” Real. It comes from Feynman’s talk “What Is Science?”, given to science teachers in 1966 and published in The Physics Teacher in 1969.
• Real “The first principle is that you must not fool yourself — and you are the easiest person to fool.” Real, word for word. It comes from Feynman’s 1974 Caltech commencement address, “Cargo Cult Science”.

How we check: we look for the original book and page, lecture, letter, recording or report. Real means the words are in Feynman’s own work; paraphrased means he said something close; misattributed means someone else said it first; no reliable source found means we couldn’t trace it. Also on Feynmanpedia: myth tests.