[Fill in she instead of he as appropriate...]
"The scientist has a lot of experience with ignorance and doubt and uncertainty, and this experience is of very great importance, I think. When a scientist doesn't know the answer to a problem, he is ignorant. When he has a hunch as to what the result is, he is uncertain. And when he is pretty damn sure of what the result is going to be, he is in some doubt."
A scientific theory that withstands that kind of scrutiny for over a hundred years is a damn good theory.
(Quote is from The Pleasure of Finding Things Out, p. 146 - the book, not the TV documentary transcript of the same name.)