Our mistake is that we doubt what is certain and want to establish what is uncertain. My maxim in the study of Nature is this: hold fast what is certain and keep a watch on what is uncertain.
What a master a man would be in his own subject if he taught nothing useless!
The greatest piece of folly is that every man thinks himself compelled to hand down what people think they have known.
If many a man did not feel obliged to repeat what is untrue, because he has said it once, the world would have been quite different.
Every man looks at the world lying ready before him, ordered and fashioned into a complete whole, as after all but an element out of which his endeavour is to create a special world suited to himself. Capable men lay hold of the world without hesitation and try to shape their course as best they can; others dally over it, and some doubt even of their own existence.
The man who felt the full force of this fundamental truth would dispute with no one, but look upon another's mode of thought equally with his own, as merely a phenomenon. For we find almost daily that one man can think with ease what another cannot possibly think at all; and that, too, not in matters which might have some sort of effect upon their common weal or woe, but in things which cannot touch them at all.