Sadly, most grad students (and most professors) can't hold a candle to Feynman, Hawking or Bekenstein.
"Oh, just be like Feynman," is not a repeatable strategy for success for most folks.
> Frankly, I just don't know very many grad students who come close to "shooting too high". I'm sure this professor has met a few, but is his concern really that they are shooting themselves in the foot, or is it that grad students who take chances for big breakthroughs (and hence, usually fail) are not very useful for advancing the career of professors?
My advisor used the term "doctoral Vietnam" for the really hard topics.
He talked about the severed heads and charred skeletons that line the paths to the top of what look like "hills."
It takes a tremendous amount of arrogance or foolishness to charge up those hills and think you're going to make it to the top.
For example, tangoing with P v NP is a classic way that brilliant students in computer science leave grad school completely dejected.
They probably could have made a good contribution had they focused on something achievable.
But, you raise an interesting question: if Ph.D. students aren't going to challenge the hard problems, then who will?
I don't have a good answer to that question.
Tenured professors. Because they certainly aren't wasting their time teaching.
But if every PhD student thought they were going to be the next Einstein and tried to write a new revolutionary paper, we'll end up with a lot Universities closing doors.
You give the risky stuff to those who have proved themselves, not to the ones who have just started.
Edit: "OP" --> "you". Sorry, I didn't realize I was talking with the author. Thanks for the thoughtful reply!