What is really sad and nightmarish (and I should add, completely unfair, in every way. And I mean it -- utterly, utterly, unfair!) is that two years later, or three years later, although you will remember very well, very clearly, that there was a point in this particular scene when you hit a horrible Writer's Block from Hell, and you will also remember there was point in this particular scene where you were writing and the words dripped like magic diamonds from your fingers -- as if the Gods were speaking through you and every sentence was a thing of beauty and magic and brilliance. You can remember just as clearly that there was a point in the story, in that same scene, when the characters had turned into pathetic cardboard cut-outs and nothing they said mattered at all. You remember this very, very clearly. The problem is you are now doing a reading and you cannot for the life of you remember which bits were the gifts of the Gods and dripped from your fingers like magical words and which bits were the nightmare things you just barely created and got down on paper somehow!! Which I consider most unfair. As a writer, you feel like one or the other should be better. I wouldn't mind which. I'm not somebody who's saying, "I really wish the stuff from the Gods was better." I wouldn't mind which way it went. I would just like one of them to be better. Rather than when it's a few years later, and you're reading the scene out loud and you don't know, and you cannot tell. It's obviously all written by the same person and it all gets the same kind of reaction from an audience. No one leaps up to say, "Oh look, that paragraph was clearly written on an 'off' day."
It is very unfair. I don't think anybody who isn't a writer would ever understand how quite unfair it is.
Full interview here.