"Inconsistency among related beliefs . . .produces motivation to do whatever is easiest in order to regain cognitive consistency or consonance among beliefs."
Jones and Gerard, Foundations of Social Psychology,1967, John Wiley and Sons, at p. 42.

Leon Festinger formulated this theory "from a very general theory of 'cognitive dissonance'." (ibid., at p. 42) Festinger explored the psychological state that resulted when two cognitions were contradictory. By contradictory he meant that they "were either logically inconsistent or incompatible with the person's past experience. (ibid., at p. 190) Festinger believed that when there was inconsistency, or when there was conflict with the person's past experience, that this makes us uncomfortable enough that we'll take the simplest way out to get consistency again.

Jones and Gerard give two examples that can explained by cognitive dissonance theory. (ibid., at p. 43) One is the reaction of a religious group whose prophecy fails to come true. Research (ibid., at p. 22 ff.) has shown that if a group predicts, say, the end of the world, and at the appointed time the world does not end, the group responds to this failure of the prophecy by suggesting that their activity warded off the anticipated apocalypse, and begins to proselytize on the grounds that theirs is the effective belief system for warding off such disaster. One might have thought that failure of the prophecy would suggest that the group could not predict. But such an interpretation would produce dissonance with the group's strongest beliefs. On the other hand, the interpretation that they had successfully warded off the disaster does not produce such dissonance with their belief system.

Another example: "severe initiation leads to liking." (ibid., at p. 43) Research has shown that people exhibit greater liking of an organization that subjects them to severe initiation than to one that subjects them only to a mild initiation. This result can be explained by cognitive dissonance theory. There is conflict between the negative affect that the person experiences in response to the initiation, since the person has chosen to go through the initiation to gain entrance to the organization. This conflict produces discomfort and tension. The person can resolve this tension by justifying the initiation as "worth it" because of the positive things he or she will gain from the benefits of membership. The more effort put into the justification process, the more attachment the person has to the organization. The more difficult the initiation, the greater the need for justification. Thus the stronger the commitment to the organization.

Other examples on the site: Perceiving Racism