It is not my experience that there is a strong connection between whether or not a PhD student is "brilliant" and his staying in or leaving academia. The most

It is not my experience that there is a strong connection between whether or not a PhD student is "brilliant" and his staying in or leaving academia. The most important factors for your future academic career are intelligence, mentoring, good project choice, good self-management and always some luck with outcome. Fail in two of these and you don't have much of a chance to get your academic carrer back on track. IMO failing at least two of these factors are usually the reasons for people to leave academia that are subsumed under "lack of success". There are also many students that are successfull and leave for the money or because they are female and want to have childern before 35. Then again, I've never been at a "top tier" university, so maybe things work different in Stanford.