Cognitive dissonance is the tense feeling that occurs when we hold two equally valid, conflicting points of view. Humans generally react to cognitive dissonance by discounting one of the viewpoints, sometimes going so far as to angrily argue against it. A classic example from literature occurs in Aesop's Fables. In the story The Fox and the Grapes, a fox desperately wants some grapes that are hanging on a high, unreachable vine. When he tries and fails to reach them, the fox decides that the grapes were probably sour anyway.