Differentiation – A state in which a person maintains who they are as a person even when naturally compelled to adjust to please the person they are dating. Example: Drummer in a band meets a girl at a gig. He falls in love with the girl and quits the band to please her. The drummer lacks differentiation and, in the end, winds up with no band or girlfriend. Playing drums in the band is what makes him attractive to the girl. Once he quits, she loses interest in him. This is the opposite of Fusion.
