I have always used a few lines from Darwin as a personal mantra: "I have steadily endeavored to keep my mind free so as to give up any hypothesis, however much beloved... as soon as facts are seen to be opposed to it..... I can't remember a single first formed hypothesis which had not after a time to be given up or greatly modified. This has naturally led me to distrust greatly deductive reasoning in the mixed sciences." Psychology is a young discipline, and immature fields advance more quickly by relying on inferences from observations, many unexpected, than by trying to prove deductions from a priori conceptions. [The Darwin quote is from his Notebooks, cited in H.E. Gruber, <i>Darwin on Man</i> (1974), 400.]