I've addressed "greed," which isn't terrible in an athlete. But I think you make a good point about players on a hot streak not knowing when to listen to their bodies and minds.
I will quibble with the bolded above, that Novak was sidelined for a year with injury. He wasn't. Maximum he didn't play was from a Wimbledon loss to the end of the year. He complained of wrist after the Rio losses at OG in 2016, but did manage to make the final of USO that year, which is about 6-7 months. After losing in the 2nd round of the AO in 2017, it was the elbow. TBH, I don't think the 2 years between Majors was all injury-related. (I know this is a debate.) The burn-out after winning the FO/Nole Slam was understandable, but I always thought that it was combined with the blow of losing first round at the Rio OG, singles, then doubles, and then bailing on Mixed doubles there. All together, an emotional blow. I personally think that set him on a mental walkabout. I know his fans say it was all about injury, but the injury reports were random, conflicting, and not wholly convincing. This is why I think, like you, that the loss at the OG can do him harm for his quest at the USO. Who knows, until all is said and done, but I think he's saying he feels burnt out. Not a lot of recovery time until the USO. As you say, there is a reason that no man has done it since Laver in the 60s.
@GameSetAndMath doesn't like my comparison to Serena, but she was within 2 matches, and the strongest woman in the field at the time, and got stopped. And she didn't have to go the Olympics in between. It's a tall order, and I don't think Novak is a mental giant.