Take the bettors in the racetrack experiment. Thirty seconds before putting down their money, they had been tentative and uncertain; thirty seconds after the deed, they were significantly more optimistic ans self-assured. The act of making a final decision--in this case, of buying a ticket--had been the critical factor. Once a stand had been taken, the need for consistency pressured these people to bring what they felt and believed into line with what they had already done. They simply convinced themselves that they had made the right choice and, no doubt, felt better and it all.

-Robert B. Cialdini, Influence: The psychology of Persuasion, p.59