“One phenomenon is certain and I can vouch for its absolute certainty: the sudden and immediate appearance of a solution at the very moment of sudden awakening. On being very abruptly awakened by an external noise, a solution long searched for appeared to me at once without the slightest instant of reflection on my part-the fact was remarkable enough to have struck me unforgettably-and in a quite different direction from any of those which I had previously tried to follow.”