not everyone at MIT works all the time, but top research scientists, and successful students at top places, do work a lot.
when i was a grad student (not at MIT), i made so little money, i was a vegetarian partly to be able to afford food for my family, and partly to require less sleep needed to digest meat. I ran several miles a day to be in good physical condition. I got up before dawn every day, worked all day, played with my kids at night until they went to bed, then worked after they fell asleep from 11 until 1am. of course i made all A's, as well as teaching undergraduate classes.
i heard once some students felt it was unfair that they wound up in classes with me and another guy, since the competition was more than they could have expected.
later when i had a research grant that was too small to feed us, i sold my car to have money to continue to study.
for ten years i sat in the same place on the floor every day surrounded by books. i went to no movies, read no novels, listended to music only to relax and study better. i skipped lunch to have more time to work and save money.
still i got letters from job applications like: "at one time a student with your qualifications would have easily obtained a position here, but unfortunately now things are different."
i found good employment, but still it was decades before I could even afford to buy math books.
the point is the work is hard, the competition is intense, and the monetary rewards are small. so it is crucial to do it for the love of the work and the subject. Pick something you absolutely love working on. Otherwise it is very hard, maybe impossible, to work hard enough to succeed.
the good part is, if you do not give up, eventually you will succeed. it just does not come quickly. and even a slow student who is persistent and thoughtful, will make great progress in time.