According to Wikipedia;
Cognitive dissonance is a psychological term describing the uncomfortable tension that may result from having two conflicting thoughts at the same time, or from engaging in behavior that conflicts with one's beliefs, or from experiencing apparently conflicting phenomena.
In simple terms, it can be the filtering of information that conflicts with what you already believe, in an effort to ignore that information and reinforce your beliefs. In detailed terms, it is the perception of incompatibility between two cognitions, where "cognition" is defined as any element of knowledge, including attitude, emotion, belief, or behavior. The theory of cognitive dissonance states that contradicting cognitions serve as a driving force that compels the mind to acquire or invent new thoughts or beliefs, or to modify existing beliefs, so as to reduce the amount of dissonance (conflict) between cognitions. Experiments have attempted to quantify this hypothetical drive. Some of these have examined how beliefs often change to match behavior when beliefs and behavior are in conflict.
Have you seen this happen with a Jehovahs Witness? Where they change the Subject or come out with something outrageous, maybe even a personal attack on you rather than what your saying...
Another Quote from the same Article;
Forbidden Toy Study
In a later experiment Aronson and Carlsmith (1963) viewed cognitive justification to forced compliance in children.
The experimenter would question the child on a set of toys to gauge which toys the children liked the most and which they found the least tempting. The experimenter then chose a toy that the child really liked, put them in a room with said toy and left the room. Upon leaving the room the experimenter told half the children that there would be a severe punishment if they played with the toy and told the other half that there would be a moderate punishment.
Later, when the punishment, whether severe or moderate, was removed, the children in the moderate punishment condition were less likely to play with the toy, even though now it had no repercussion.
When questioned, the children in the moderate condition expressed more of a disinterest in the toy than would be expected towards a toy that they had initially ranked high in interest. Alternatively, the desirability of the toy went up for the children in the severe punishment condition.
This study laid out the effect of overjustification and insufficient justification on cognition.
In overjustification, the personal beliefs and attitudes of the person do not change because they have a good external reason for their actions. The children threatened with the severe punishment had a good external reasoning for not playing with the toy because they knew that they would be badly punished for it. However, they still wanted the toy, so once the punishment was removed they were more likely to play with it. Conversely, the children who would get the moderate punishment displayed insufficient justification because they had to justify to themselves why they did not want to play with the toy since the external motivator, the degree of punishment, was not strong enough by itself. As a result, they convinced themselves that the toy was not worth playing with, which is why even when the punishment was removed they still did not play with the toy.