Anna Quindlen, in The Agony of Writing:
I don’t believe in writer’s block. It’s not that sometimes you can’t write, it’s that you can’t write* well. Experience has told me that writing poorly sometimes leads to something better. Not writing at all leads only to reruns of “Law and Order.” Which I love, but still.
(At the end of a day’s writing), I always stop in mid-sentence. Starting a new chapter or a new paragraph first thing in the morning might be too much to bear. But I can always manage to finish a sentence. And one sentence has a way of following another if everything else around me is routine enough.
*Or design. (sic)