Insufficient Justification Effect
The insufficient justification effect is a theory proposed by Festinger and Carlsmith that attempts to explain how individuals deal with cognitive dissonance. Cognitive dissonance is an unpleasant state of mind that occurs when two conflicting beliefs or thoughts are held at the same time. The insufficient justification effect is when a person finds an internal cause for an explanation to a behavior because there isn't an external cause. This effect reduces cognitive dissonance be justifying a behavior internally when there is insufficient external justification.
For example, in an experiment by Festinger and Carlsmith participants performed a really boring task. Afterwards they were asked to be dishonest to the next participant by lying about how fun and entertaining the task was. One group of participants was given $1 for lying while another group was given $20 to lie. They found that the $1 group rated the task as being a lot more fun than the $20 group. The insufficient justification effect occurred. Both groups needed a justification for being dishonest: the $20 group had an external justification (getting $20) while the $1 group didn't so they developed an internal justification (that the task was more fun than it actually was).