It drives off a reasonable number of high-performing people as well, though obviously not all. One of the problems systems like stack ranking have encountered is that some proportion of people who are really good and not the intended target of the system end up very stressed out by it. Varying reasons: some people underestimate their own skills, some are worried about the system's false-positive rate, some are stressed out by worries about coworkers being fired even if not worried about their own job, etc.