According to an old roommate of mine, a PhD is merely a pass-fail
paper. Somehow it took me 7 years of graduate school to
complete the all-nighter necessary for cranking out such a paper.
As quoted in David Warsh's book, Knowledge and the Wealth of Nations, Paul Romer, a well-known economist, had a nice quote about the ups and downs of research. This is one of the best descriptions I've read of the process of research, at least as I experience it, though I unfortunately can't claim that my results are anywhere near as profound as those of Paul Romer:
The first interaction I can remember is playing with some control theory model and coming to the first recognition that there was a way to get at growth if I built in some increasing returns. The next thing I remember is one of these episodes, pencil and yellow pad. When you do that, there are all these ups and downs in the process, sometimes you think you've really got it, other times you think you're at a dead end. I remember trying to go to bed one night at a point where I had some success, because it's hard to relax when you think it's all falling apart. There's this pacing you try to do, you try to quite before it can all fall apart again.... The moment (that) you look for is when you reach a kind of completion. You don't want to interrupt when things are progressing, when you've tied off a piece. I remembered somebody's description of the life of a poet: you are only a poet at the moment you finish the last line in the poem. Before then, you are a failed poet; after that, you are an ex-poet. At those moments of completion, I felt like an economist.