“The scientist explores the world of phenomena by successive approximations. He knows that his data are not precise and that his theories must always be tested. It is quite natural that he tends to develop healthy skepticism, suspended judgment, and disciplined imagination — not only about other people's ideas but also about his own.”
- Edwin Hubble
Adding this one to the list of similar quotes from scientists and thinkers that includes Albert Einstein (here and here), Richard Feynman and Karl Popper.
(NB: The italics indicate the latter part of the quote may have been added by others.)