"Have you noticed how often it happens that a really good idea -- the kind of idea that looks, as it approaches, like the explanation for everything about everything -- tends to hover near at hand when you are thinking hard about something quite different? There you are, halfway into a taxi, thinking about the condition of the cartilage in the right knee joint, and suddenly, with a whirring sound, in flies a new notion looking for a place to light. You'd better be sure you have a few bare spots, denuded of anything like thought, ready for its perching, or it will fly away into the dark."
— Lewis Thomas (The Youngest Science)