People sometimes accuse me of knowing a lot. "Stephen," they say, accusingly, "you know a lot." This is a bit like telling a person who has a few grains of sand clinging to him that he owns much sand. When you consider the vast amount of sand there is in the world such a person is, to all intents and purposes, sandless. We are all sandless. We are all ignorant. There are beaches and deserts and dunes of knowledge whose existance we have never even guessed at, let alone visited.