Where it comes from
After the Space Shuttle Challenger was lost in 1986, Feynman served on the presidential commission that investigated the accident. His own conclusions went into the report as a separate appendix, Appendix F, “Personal observations on the reliability of the Shuttle”. The famous sentence is its very last line.
What led up to it
The appendix is about one question: how likely is it that a shuttle will be lost? Feynman found that the answers depended on whom you asked. “The estimates range from roughly 1 in 100 to 1 in 100,000. The higher figures come from the working engineers, and the very low figures from management.”
He did the arithmetic on the optimistic number: 1 in 100,000 “would imply that one could put a Shuttle up each day for 300 years expecting to lose only one”. And he asked: “What is the cause of management’s fantastic faith in the machinery?”
His conclusions put the engineers’ view at a chance of failure “of the order of a percent”, while official management claimed to believe it was “a thousand times less”. The appendix ends by saying NASA owes the citizens who fund it frank, honest and informative answers, and then: “For a successful technology, reality must take precedence over public relations, for nature cannot be fooled.”
Our take
Real, and one of the best-sourced Feynman lines there is, because it sits in a government report you can read online. It now turns up on slides about honesty in business, and that’s fair. But the original had a precise target: the gap between what engineers measured and what managers said. The physics didn’t care which number was more convenient.
It’s also the same idea as his 1974 line “you must not fool yourself”, applied to an organisation instead of a person.
