The line comes from Lewis Carroll's Alice's Adventures in Wonderland, where the Cheshire Cat tells Alice that everyone in Wonderland is mad, and it became widely known through Disney's 1951 animated film Alice in Wonderland, with Sterling Holloway voicing the grinning cat. The exchange has survived as a shorthand for cheerful irrationality, quoted in books, films and internet memes whenever logic breaks down. Its appeal endures because it is short, instantly recognisable and affectionate rather than insulting, turning madness into a shared joke.