Once two cognitions are held and there is a conflict between them, one falls into a state of cognitive dissonance. This may be demonstrated by someone purchasing a brand of washing machine, initially believing that it was the best product to buy. One's cognition is that a good washing machine has been bought. However, after the purchase, one may be exposed to another cognition informing one that there is a better washing machine out on the market (for example, through an advertisement). This then leads to an imbalance between cognitions and a psychological state which needs to seek consonance between the two cognitions.

Two kinds of dissonance:

Theorists have identified two different kinds of cognitive dissonance that are relevant to decision making: pre-decisional dissonance and post-decisional dissonance.

Pre-decisional dissonance might be analogous to what Freud called "compensation." When a test showed that subjects had latent sexist attitudes, they later awarded a female a larger reward than a male in what they were told was a different study. Researchers hypothesized that the larger reward reduced dissonance by attempting to show that they were not sexist in the later decision, not considering the possibility that the subjects were trying to influence the attitudes of the testers instead of performing mysterious internal mental gymnastics to relieve hypothetical stress.

The more well-known form of dissonance, however, is post-decisional dissonance. Many studies have shown that people with compulsive disorders like gambling will subjectively reinforce decisions or commitments they have already made. In one simple experiment, experimenters found that bettors at a horse track believed bets were more likely to succeed immediately after being placed. According to the hypothesis, the possibility of being wrong is dissonance-arousing, so people will change their perceptions to make their decisions seem better.

This ignores the fundamental principle in decision making, that a decision is to be made if it will produce a better outcome than the alternatives. It also ignores the known potential of afterthought to produce novel thinking that dispels impulse behaviour. This is the basis of the foot-in-the-door technique in sales, and possibly confirmation bias.

Post-decisional dissonance may be increased by the importance of the issue, the length of time the subject takes to make or avoid the decision, and the extent to which the decision could be reversed.

Further Propositions by Festinger:

Festinger proposed that cognitive dissonance is a "negative drive state", a similar psychological tension to hunger and thirst and that people will seek to resolve this tension.

Reduction of cognitive dissonance, Festinger believed, is good because one feels better, and because one can come closer to consonance by eliminating contradictions. On the other hand some of the ways of reduction of cognitive dissonance involve a distortion of the truth, which may cause wrong decisions. The harder way of changing favourable cognitions may in the longer run be better.

When confronted with two belief cognitions that contradict each other, Festinger suggests the dissonance can be resolved by finding and adding a third piece of information relevant to the two beliefs. For example, if Sam believes that elected officials are trustworthy, but also believes that elected officials have broken his trust, then the cognitive dissonance can be resolved by discovering that all elected officials lie. This enables Sam to (it is to be hoped) still hold that elected officials are still largely trustworthy, but that they also all lie.