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.
Work gives you meaning and purpose and life is empty without it.
There's no regret. You can't regret. I mean I've felt regret but I've also...
My work is about my life and what I want to do with it.
