'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: Alice's Adventures in Wonderland and Through the Looking Glass, Pages: Chapter 6
Contributed by: Tsuya