In his book The Swann's Way, the French novelist Marcel Proust wrote of returning home late one evening on a dull winter day when he faced the prospect of a depressing tomorrow. The maid greeted him and, seeing that he was tired, brought him a cup of hot tea and some cake. Being both tired and depressed he at first refused them. Only at her insistence did he finally begin to drink the tea and eat the cake. Proust wrote that an unexplainable delight suddenly came over him. His anxieties and troubles seemed to vanish. Suddenly, he wrote, I had "ceased to feel mediocre, accidental and mortal."

What caused this wonderful sensation to come over him? He was at a loss to explain it. How could a …