This article assumes that talent and an assertive ego go hand in hand. There may be two star players in terms of talent, where one views everything as a competition, and the other may be more self-competitive. I wonder if you try to redirect the competitive ego, or try to build up the less extroverted one?
Usually if a star player leaves everybody wonders how they'll get by without him (it's always a him) and then they find out things actually become easier...