"Brick walls are there to stop the people who don't want it badly enough."
      -- Randy Pausch, The Last Lecture

A Ph.D. filters out people who do not want to be a scientist enough whilst training the doctoral candidate in the "publish or perish" mantra that now prevails.

But for every smart observation there are exceptions: Fields medal recipient (well, he won it but rejected to take it) G. Perelman (born 1966 and jobless last time I checked) has almost no publications or citations to show. But he will be remembered forever for proving the Poincaré conjecture ( https://en.wikipedia.org/wiki/Grigori_Perelman ).