"Alice tried another question. "What sort of people live about here?" "In THAT direction," the Cat said, waving its right paw round, "lives a Hatter: And in THAT direction," waving the other paw, "lives a March Hare. Visit either you like: they're both mad." "But I don't want to go among mad people," Alice remarked. "Oh, you can't help that," said the Cat: "we're all mad here. I'm mad. You're mad." "How do you know I'm mad?" said Alice. "You must be," said the Cat, "or you wouldn't have come here.""

Source: Lewis Carroll (2001). “CliffsComplete Alice's Adventures in Wonderland”, Cliffs Notes