What is Cognitive Dissonance?

Legal Definition
In psychology, cognitive dissonance is the mental stress or discomfort experienced by an individual who holds two or more contradictory beliefs, ideas, or values at the same time; performs an action that is contradictory to their beliefs, ideas, or values; or is confronted by new information that conflicts with existing beliefs, ideas or values.

Leon Festinger's theory of cognitive dissonance focuses on how humans strive for internal consistency. An individual who experiences inconsistency tends to become psychologically uncomfortable, and is motivated to try to reduce this dissonance, as well as actively avoid situations and information likely to increase it.
-- Wikipedia
Legal Definition
Incompatibility among a person's attitudes, behavior, beliefs, and/or knowledge results in a state of psychological tension. Also occurs when a choice has to be made between equally attractive or repulsive alternatives. An example is 'buyer's remorse,' a feeling one experiences consisting of guilt associated with doubts about the reasonableness of a purchase decision after making an expensive purchase. Testimonials, money back guaranties, and after-sales service are ways that marketers try to mitigate buyer's doubts through supportive information. Contrasts with cognitive consonance.