Alice laughed: “There’s no use trying,” she said; “one can’t believe impossible things.”
“I daresay you haven’t had much practice,” said the Queen. “When I was younger, I always did it for half an hour a day. Why, sometimes I’ve believed as many as six impossible things before breakfast.”
Lewis Carroll (Charles Lutwidge Dodgson), Through the Looking Glass, Chapter V, “Wool and Water.” 1871 (Gutenberg edition)
Below the fold; the quote in larger context.