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 one or more beliefs, ideas or values, or is confronted by new information that conflicts with existing beliefs, ideas, or values.
In ’57 Leon Festinger publishes “A theory of cognitive dissonance” (Stanford University Press, 1957). In this work he postulates about the conflicts that occur when we hold contradictory opinions, such as believing little children should be quiet, at the same time as being proud when their child gains attention.
This conflict results in a reduction in thought that modifies the understanding to suit the position. “I know smoking causes cancer, but i still smoke.” Inevitably the thought reduction is a denial of truth to suit the position.
This cartoon from Dilbert sums it up nicely: