Wikipedia | Project Gutenberg

(Yes, I had never read it until just now.)

I must quote my favorite line:

“I quite agree with you,” said the Duchess; “and the moral of that is—‘Be what you would seem to be’—or, if you'd like to put it more simply—‘Never imagine yourself not to be otherwise than what it might appear to others that you were or might have been was not otherwise than what you had been would have appeared to them to be otherwise.’”