There's a wonderful Barthes essay about the pain of revision called "Flaubert and the Sentence" in his New Critical Essays (Hill and Wang, 1980):

...Flaubert subtracts, erases, constantly returns to zero, begins over again. Flaubertian sequestration has for its center (and its symbol) a piece of furniture which is not the desk but the divan: when the depths of agony are plumbed, Flaubert throws himself on his sofa: this is his "marinade," an ambiguous situation, in fact, for the sign of failure is also the site of fantasy, whence the work will gradually resume, giving Flaubert a new substance which he can erase anew. Flaubert qualifies this Sisyphean circuit by a very strong word, "atrocious," the sole recompense he receives for his life's sacrifice.

Also:

...style for Flaubert is absolute suffering, infinite suffering, useless suffering.

Why writing poetry is hard:

For it is indeed a matter of vertigo: correction is infinite, it has no sure sanction.

Why writing fiction is worse:

I have a narration to compose; now the story is something which is very wearisome for me. I have to send my heroine to a ball.

Man, I love this stuff.