Cognitive dissonance
Cognitive dissonance is a discomfort caused by holding conflicting idea
In the most narrow sense, an idea is just whatever is before the mind when one thinks. Very often, ideas are construed as representational images; i.e. images of some object. In other contexts, ideas are taken to be concepts, although abstract concepts do not necessarily appear as images...

s simultaneously. The theory of cognitive dissonance proposes that people have a motivational drive
Drive theory
The terms drive theory and drive reduction theory refer to a diverse set of motivational theories in psychology. Drive theory is based on the principle that organisms are born with certain physiological needs and that a negative state of tension is created when these needs are not satisfied...

 to reduce dissonance. They do this by changing their attitudes, beliefs, and actions. Dissonance is also reduced by justifying, blaming, and denying. The phrase was coined by Leon Festinger in his 1956 book When Prophecy Fails
When Prophecy Fails
When Prophecy Fails is a 1956 classic book in social psychology by Leon Festinger, Henry Riecken, and Stanley Schachter about a UFO religion that believes the end of the world is at hand.- Cognitive dissonance :...

, which chronicled the followers of a UFO cult as reality clashed with their fervent beliefs.