if you do something contrary to your beliefs or attitudes, you will
experience the most cognitive dissonance when the amount of reward of
justification for action is:

Small.  "In the classic dissonance experiment, lying for a small,
rather than a large, reward was shown to change attitudes toward the
object of the lie."

Psychology and Life, 12th edition, Philip G. Zimbardo, Scott, Foresman
& Co., 1985, page 619

Sincerely,

Wonko