A manager I know had a term for obnoxious over-achievers: "brilliant assholes". But there are other kinds of high achievers who should not leave because, after all, talent is talent. You don't say, "Bob wrote 70% of our product, and he's head and shoulders above the rest of the team, so he's got to go!" You should say, "How are we best utilizing our in-house talent? Does Bob engender resentment from the lesser progra…
This question definitely captures more of the nuance that I felt was naggingly lacking in the original post. It's easy to justify firing someone in very black and white terms, but it's a lot harder to take such an employee and turn them into a valuable member of the team again, even though that might be the best outcome. Not saying it can always be done -- I've seen managers try for too long and fail, but I've also seen managers start making cuts at the first sign of trouble.