Here’s a peg. Screw it in this hole a quarter turn. Repeat. Again. Repeat. For an hour. As intended, this task is boring. Really, mind-numbingly boring. And after an hour any sane person has learned to hate it. But what if after spending an hour doing this, you were paid $20 to convince the next subject that the task is actually pretty fun? What if you were paid only $1 to sucker the next guy in?
How does the amount of money you were paid affect your feelings about the task itself? You probably remember the task a little more fondly if you got twenty bucks for it, right?
Nope.
Being paid $20 allows you to blame your behavior (convincing someone the task is fun) on the money, whereas if you earn only a buck, you have to otherwise justify your behavior—you convince yourself, at least in part, that turning pegs for an hour is fun. In other words, being paid allows you to say “that sucked but at least I got paid,” while without money, you have to tell yourself “I guess it really wasn’t that bad.”
And what you tell yourself becomes your belief.