Explain the process know as "cognitive dissonance"

Cognitive dissonance is a discomfort caused by holding conflicting cognitions (e.g., ideas, beliefs, values, emotional reactions) simultaneously. In a state of dissonance, people may feel surprise, dread, guilt, anger, or embarrassment.[1] The theory of cognitive dissonance in social psychology proposes that people have a motivational drive to reduce dissonance by altering existing cognitions, adding new ones to create a consistent belief system, or alternatively by reducing the importance of any one of the dissonant elements.[1]