Cognitive dissonance is a discomfort caused by holding conflicting cognitions (e.g., ideas, beliefs, values, emotional reactions) simultaneously. In a state of dissonance, people may feel surprise, dread, guilt, anger, or embarrassment. The theory of cognitive dissonance in social psychology proposes that people have a motivational drive to reduce dissonance by altering existing cognitions, adding new ones to create a consistent belief system, or alternatively by reducing the importance of any one of the dissonant elements. An example of this would be the conflict between wanting to smoke and knowing that smoking is unhealthy; a person may try to change their feelings about the odds that they will actually suffer the consequences, or they might add the consonant element that the smoking is worth short term benefits. A general view of cognitive dissonance is when one is biased towards a certain decision even though other factors favour an alternative.
The phrase was coined by Leon Festinger in his 1956 book When Prophecy Fails, which chronicled the followers of a UFO cult as reality clashed with their fervent belief in an impending apocalypse. Cognitive dissonance is one of the most influential and extensively studied theories in social psychology. Cognitive disequilibrium is a closely related concept in the cognitive developmental theory of Jean Piaget: the inevitable conflicts a child experiences between current beliefs and new information will lead to disequilibrium, which in turn motivates the child’s progress through the various stages of development.
Cognitive dissonance theory warns that people have a bias to seek consonance among their cognitions. According to Festinger, we engage in a process he termed “dissonance reduction”, which he said could be achieved in one of three ways: lowering the importance of one of the discordant factors, adding consonant elements, or changing one of the dissonant factors.  This bias gives the theory its predictive power, shedding light on otherwise puzzling irrational and even destructive behavior. But it doesn’t tell us if the ufo behind the comet Hale-Bopp was picking up travellers and just forgot to ‘spade under’ the earth on its way, because it was in a hurry, because of trouble with the comet’s tail, or what.