Chemotherapy is brutal. The goal is pretty much to kill everything in your body without killing you.
It is no good getting furious if you get stuck. What I do is keep thinking about the problem but work on something else. Sometimes it is years before I see the way forward. In the case of information loss and black holes, it was 29 years.
I find that it's nice to work with somebody and spin off on someone else's feelings. You get a little jaded by yourself.