"Remember the story of Poincare? No, not the politician, the mathematician. He would send his students to the blackboard, and after they had used up a good dozen pieces of chalk on meter-long equations, he would ask them to leave the chalk and board, turn toward the other students and briefly explain, in simple language, what they had just calculated. If they couldn't, he would stick them with horrible grades, for he wasn't a kind man. Above all, he firmly believed that physics should be popular (his word), thus understandable by most."
-- Jean Emile Charon