The Cuckoo's Nest.

"Because he knows you have to laugh at the things that hurt you just to keep yourself in balance, just to keep the world from running you plumb crazy. He knows there's a painful side; he knows my thumb smarts and his girl friend has a bruised heart and the doctor is losing his glasses, but he won't let the pain blot out the humor no more'n he'll let the humor blot out the pain."