“The first principle is that you must not fool yourself — and you are the easiest person to fool.”
" Cargo Cult Science http://calteches.library.caltech.edu/51/2/CargoCult.htm", adapted from a 1974 Caltech commencement address; also published in Surely You're Joking, Mr. Feynman!, p. 343
Variant: The first principle is that you must not fool yourself — and you are the easiest person to fool.
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Richard Feynman 181
American theoretical physicist 1918–1988Related quotes

“Don’t fool yourself that you are going to have it all. You are not.”
The Successful Woman : How You Can Have a Career, a Husband, and a Family — and Not Feel Guilty About It (1988), p. 18
Context: Don’t fool yourself that you are going to have it all. You are not. Psychologically, having it all is not even a valid concept. The marvelous thing about human beings is that we are perpetually reaching for the stars. The more we have, the more we want. And for this reason, we never have it all.

Dogs
The Note-Books of Samuel Butler (1912), Part XIV - Higgledy-Piggledy
“I was foolish because I believed in you. You are a fool because you believe in yourself!”
Source: In Search of Satisfaction