It starts off as a generic 'kicking out the party member that secretly carries the party' plot saying he's weak, doesn't carry his own weight, that he's dragging down the team, y'know, all the good stuff. But it turns out that the party kicked him out becuse
they were dragging
him down and they wanted him to fulfill his talent and go on to do great things.
He does however, still swear to go on a violence fueled revenge spree and destroy his former party