From Gary North’s The Ph.D. Glut Revisited:
If wishes were horses, beggars would ride. Also, if ego were marketable, all Ph.D. graduates would get tenure.Why does any Ph.D. student at any but the top graduate schools believe that he will get tenure at any university? The odds are so far against him, and have been for a generation, than he ought to realize that he is about to waste his most precious resource – time – on a long-shot. Investing five or more years beyond the B.A. degree, except in a field where industry hires people with advanced degrees, is economic stupidity that boggles the imagination. Yet at least 200,000 graduate students are doing this at any time. Of the 46,000 who earned a Ph.D. in 2003, at least 50% got to ABD status and quit. Probably more than half of the others quit before they got to ABD status.
At $20,000 or more per year in tuition and living expenses, plus the $35,000 not earned in the job market, trying to earn a Ph.D. is a losing proposition.