Cognitive Dissonance occurs when a person attempts to hold two contradictory ideas in their head simultaneously and in my opinion leads to insanity.

I've found Cognitive Dissonance to be a very useful explanation for a lot of behavior I've witnessed in my life on a personal, social, and political scale. I've wondered hard and long about why people seemed to do such silly things over and over again when it was obvious to me how dysfunctional or suboptimal some people's thoughts and actions were. It seems that there is the desire of the majority of people to maintain the status quo and to endeavor to find paths to the older and more comfortable ways regardless of the downside of those choices. Like, justifying the short-term benefits of industrialization over the long-term detrimental effects to the environment.

"Doublethink" is another term denoting the act of holding two contradictory beliefs simultaneously and fervently believing both.

"True-Believer Syndrome" demonstrates carrying a post-cognitive-dissonance belief regardless of new information.

"Effort Justification" is the tendency to attribute a greater value (greater than the objective value) to an outcome that they had to put effort into acquiring or achieving and thus never end up resolving the dissonance. The effect of rites of passage and hazing rituals on group solidarity and loyalty, prevalent in military units, sports teams and academic fraternities and sororities, often include demanding and/or humiliating tasks which lead (according to dissonance theory) the new member to increase the subjective value of the group which contributes to his/her loyalty and to the solidarity of the entire group.

"Choice-Supportive Bias" is a tendency to retroactively ascribe positive attributes to a choice that a person has made in the past. For example, researchers have used written scenarios in which participants are asked to make a choice between two options. Then later, on a memory test, participants are given a list of positive and negative features, some of which were in the scenario and some of which are new. A choice-supportive bias is seen when both correct and incorrect attributions tend to favor the previously chosen option, with positive features more likely to be attributed to the chosen option and negative features to the rejected option. Giving people false reminders about which option they chose in a previous experiment session led people to remember the option they were told they had chosen as being better than the other option. This reveals that choice-supportive biases arise in large part when remembering past choices, rather than being the result of biased processing at the time of the choice. Older adults are more likely than younger adults to show choice-supportive biases, which may be related to older adults' greater tendency to show a positivity effect in memory. Choice-supportive bias is potentially related to the aspect of cognitive dissonance as post-decisional dissonance. Within the context of cognitive dissonance, choice-supportive bias would be seen as reducing the conflict between "I prefer X" and "I have committed to Y".

Dissonance normally occurs when a person perceives a logical inconsistency among his or her cognitions. This happens when one idea implies the opposite of another. For example, a belief in animal rights could be interpreted as inconsistent with eating meat or wearing fur. Noticing the contradiction would lead to dissonance, which could be experienced as anxiety, guilt, shame, anger, embarrassment, stress, and other negative emotional states. When people's ideas are consistent with each other, they are in a state of harmony, or consonance. If cognitions are unrelated, they are categorized as irrelevant to each other and do not lead to dissonance.

A powerful cause of dissonance is an idea in conflict with a fundamental element of the self-concept, such as "I am a good person" or "I made the right decision." The anxiety that comes with the possibility of having made a bad decision can lead to rationalization, the tendency to create additional reasons or justifications to support one's choices. A person who just spent too much money on a new car might decide that the new vehicle is much less likely to break down than their old car. This belief may or may not be true, but it would likely reduce dissonance and make the person feel better. Dissonance can also lead to confirmation bias, the denial of disconfirming evidence, and other ego defense mechanisms.

The "ideas" or "cognitions" in question may include attitudes and beliefs, the awareness of one's behavior, and facts. The theory of cognitive dissonance proposes that people have a motivational drive to reduce dissonance by changing their attitudes, beliefs, and behaviors, or by justifying or rationalizing their attitudes, beliefs, and behaviors. Cognitive dissonance theory is one of the most influential and extensively studied theories in social psychology.