The Brain (according to Tom Robbins)

 
If little else, the brain is an educational toy. While it may be a frustrating plaything -- one whose finer points recede just when you think you are mastering them -- it is nonetheless perpetually fascinating, frequently surprising, occasionally rewarding, and it comes already assembled; you don't have to put it together on Christmas morning.

The problem with possessing such an engaging toy is that other people want to play with it, too. Sometimes they'd rather play with yours than theirs. Or they object if you play with yours in a different manner from the way they play with theirs. The result is, a few games out of a toy department of possibilities are universally and endlessly repeated. If you don't play some peoples games, they say you have "lost your marbles," not recognizing that, while Chinese checkers is indeed a fine pastime, a person may also play dominoes, chess, strip poker, tiddlywinks, drop-the-soap or Russian roulette with his brain.

One brain game that is widely, if poorly, played is a gimmick called 'rational thought'."

 [from Even Cowgirls get the Blues, (p.133). 1976 Bantam reissue, October 1993]