To rid himself of unconscious feelings of profound identity shame caused by his dysfunctional family of origin, a narcissist will create an idealized false self to disprove the damage.  To confirm this idealized self-image, he will also project his damaged identity onto someone else who will carry the shame for him. To prove to himself that he has gotten rid of all that unwanted shame, the narcissist will seek to rule over and humiliate that person, proving to himself that his idealized self-image has triumphed over the damaged self image. Sometimes two people will trade the shame back and forth in regular competition to be the winner rather than the humiliated loser.

Read the full article here:  Shame Trading