Cognitive Dissonance

Definition: Cognitive Dissonance is the feeling of discomfort when simultaneously holding two or more conflicting cognitions: ideas, beliefs, values or emotional reactions.
It is a consistency theory by Festinger ('57), who argued that people will look for information that is likely to confirm and support existing attitudes and views, avoiding simultaneously information that is incongruent to existing attitudes and views.
Two ideas that are consistent are consonant. If they are inconsistent they are dissonant. And if they are unrelated or unconnected they are irrelevant.
Dissonance initiates an uncomfortable feeling that leads towards attitude change.
See also confirmation bias in decision making.

More on cognitive dissonance. More on individual decision making: Anchoring Bias, Bayesian Theory, Black Swan Theory, Bounded Rationality, Cognitive Bias, more...