Caught this on Deadspin: http://deadspin.com/my-injury-file-how-i-shot-smoked-and-screwed-my-way-1482106392
Link takes you to an excerpt that talks about the toll playing football takes on human bodies. The excerpt's from Nate Jackson's book on his NFL career, which may not be typical of NFL careers but isn't exactly strange. The point about the injuries is that ignoring one leads to another, and rehabbing that instead of fixing it leads to another, and etc. etc.
Hot Take: Since we talk about what's in it for the kids all the time, I guess it lends some perspective to remember these guys have to spend the next 60 years paying for their football careers.