[qiqing]

There's also something else at play that isn't just "cream rises."

If you're a top student who chose a slightly suboptimal grad school for personal reasons (to be near a significant other, taking care of a family member, already have a house somewhere, etc.), you may not realize that the game became cripplingly hard for you until you're near the end of your program.

The top universities often: (1) send grad students to conferences (including travel costs) whether or not they have results to present that year, (2) hire lab techs and admins, which allows grad students more time to do actual research, and (3) make it more likely that the student gets a grant proposal accepted by the NIH/NSF/other agency.

And you know, maybe you hold out hope because your advisor let you and your lab mates volunteer stuffing all the swag bags the night before a conference that happens to be in your city that year so you can go talk to all the other folks at the top of your field. Maybe you actually get a grant funded, unlike your classmates. Maybe you put in that many more hours so you can handle your share of the grunt work on top of research you'll actually get published. No weekends for five years. Do you do it? Maybe.

[tsotha]

You might do it if you were sure you'd actually land on the tenure track and get tenure. That's far from assured, though. Seems like most people reach 35 or 40 before they're officially denied tenure, meaning you've wasted your most productive years chasing a career that's not going to happen.