Novels aren’t written, they’re rewritten. It is one of the hardest things to accept, especially after the seventh rewrite hasn’t quite done it.

Michael Crichton (1942-2008) American author, producer, director, and screenwriter

(Attributed)

Crichton was quoted a number of times on the adage, which he in turn claimed was in more general use. However, he seems to have been key in popularizing it. See here for more discussion and specific citations.