Fear is a vital response to physical and emotional danger—if we didn't feel it, we couldn't protect ourselves from legitimate threats. But often we fear situations that are far from life-or-death, and thus hang back for no good reason. Traumas or bad experiences can trigger a fear response within us that is hard to quell.
If you've ever told a lie and felt uncomfortable because you see yourself as scrupulously honest, then you've experienced cognitive dissonance. It occurs whenever your view of yourself clashes with your performance in any area—you see yourself as smart but can't believe you made such dumb stock investments.