Cognitive dissonance is an uncomfortable feeling caused by holding conflicting ideas simultaneously. The theory of cognitive dissonance proposes that people have a motivational drive to reduce dissonance. They do this by changing their attitudes, beliefs, and actions. Dissonance is also reduced by justifying, blaming, and denying. It is one of the most influential and extensively studied theories in social psychology. A closely related term, cognitive disequilibrium, was coined by Jean Piaget to refer to the experience of a discrepancy between something new and something already known or believed.
Experience can clash with expectations, as, for example, with buyer’s remorse following the purchase of an expensive item. In a state of dissonance, people may feel surprise, dread, guilt, anger, or embarrassment. People are biased to think of their choices as correct, despite any contrary evidence. This bias gives dissonance theory its predictive power, shedding light on otherwise puzzling irrational and destructive behavior.
A classical example of this idea (and the origin of the expression “sour grapes“) is expressed in the fable The Fox and the Grapes by Aesop (ca. 620–564 BCE). In the story, a fox sees some high-hanging grapes and wishes to eat them. When the fox is unable to think of a way to reach them, he surmises that the grapes are probably not worth eating, as they must not be ripe or that they are sour. This example follows a pattern: one desires something, finds it unattainable, and reduces one’s dissonance by criticizing it. Jon Elster calls this pattern “adaptive preference formation.”
source: Cognitive Dissonance