Why do we attempt to justify decisions that are clearly irrational? The answer lies in "cognitive dissonance," the feeling of mental discomfort we experience when we hold two contradictory beliefs at the same time. American social psychologist Leon Festinger believed that we have developed mechanisms to try to deal with the stress brought on by holding incompatible beliefs. So we change existing attitudes, adjust their relative importance, or accept dubious evidence to justify our choices in order to rationalize and justify actions after the event. Research on dissonance has been very important in encouraging sociable behavior, promoting healthy habits, and reducing prejudice.