I think this, from David Mitchell, is brilliant on self-editing. He said it during the Humber School for Writers Summer Workshop in 2009:
A consolation: as you perform the necessary editing, it really hurts. “I love that line, its such a neat bit, its brilliant!” Brilliant isn’t actually enough–its got to be brilliant, and have a place there. And oddly enough, you cut it, but in a weird way, its still there. It’s gone but it hasn’t actually gone. It’s still there in your denser, and your richer and your better text. It’s in the texture. Books are palimpsests of your earlier drafts. So don’t be too disheartened because its gone, because it isn’t really. Or to give you some Confucianism: what the pruning shears remove remains on the tree in its enhanced vigour. A good rule of thumb: if you have to think more than five seconds about whether or not a thing should be cut, that means do it. In the age of word processors, I’ve got a file called “may be useful one day,” where I put things that are great and that I can’t bear to lose. I cut and paste and put it in the file, so at least its there in case I ever want to go back and retrieve it. How often do I go back and retrieve it? Never. Not once. Which I feel proves my point.