You kind of missed your own (or possibly your professor's) point there: being great at something is a matter (in part) not just of putting in the work, but of having the inclination and motivation to put in so much work. If you think of it as "all the toil that gets you to that level", you're not the kind of person who is going to become great in that field.
The people with variable work ethic, but who could be motivated by the subject matter itself, mastered the subject and ended up with the remunerative careers "by accident."
You have to be willing to do the work, yes, but also figure out what you really, really like doing, and then do it -- a lot. Over, and over, and over, for years or even decades.
That being said, running after high remuneration in and of itself isn't bad. Sometimes its just what you have to do because a lot of other people depend on it.
The professor's point was, being great at something isn't just a matter of having a big powerful brain, it's also a result of putting in the work, and that work is not glamorous. A lot of people want to go straight to the big, fun, "important" problems, the big job titles and pay checks, while skipping all the toil that gets you to that level.