If the waitress brings by another basket of hot, fresh tortilla chips right out of the oil - they may seem so yummy that you're tempted to have just one more. But no - you really have had your last tortilla chip after all.
Some people like to call this diminishing marginal utility - but really, it's all about tortilla chips.
T.
P.S. Absolutely unrelated, great Dilbert blog today:
http://dilbertblog.typepad.com/the_dilbert_blog/2006/11/blame_room_serv.html