Calvin and Hobbes by Bill Watterson for December 23, 1987
Calvin: Well, I've decided I do believe in Santa Claus, no matter how preposterous he sounds. Hobbes: What convinced you? Calvin: A simple risk analysis. I want presents, lots of presents. Why risk not getting them over a matter of belief? Heck, I'll beleive anything they want. Hobbes: How cynically enterprising of you. Calvin: It's the spirit of Christmas.