My answer to the questions: 'How do you know? What is the source of the basis for your assertion? What observations have led you to it?' would be: I do not know: my assertion was merely a guess. Never mind the source or the sources, from which it may spring. There are many possible sources, and I may not be aware of half of them; and origins and pedigrees have in any case little bearing upon truth. But if you are interested in the problem which I tried to solve by my tentative assertion, you may help me by criticizing it as severely as you can; and if you can design some experimental test which you think might refute my assertion, I shall gladly, and to the best of my powers, help you to refute it."    

- Karl Popper