Early on in the book, Knight talks about the four stages of a writer's development. It's an analysis that's worthwhile sharing:
Stage 1. You are writing for yourself, and your stories are essentially daydreams. They please you in a sort of narcissistic way, but they are not stories that communicate to other people.
Stage 2. You are trying to break out of the shell, trying to communicate, but your stories are what editors call "trivial." You are not yet ready to write a completely developed story, and you're trying to get away from half-formed ones. The rejection slips tell you that you're not succeeding.
Stage 3. You are writing complete stories, or reasonable imitations, but you are being held back by technical problems, usually weaknesses in structure or character.
Stage 4. You have solved these problems, at least well enough to get by, and now you are working on a professional level.
Knight acknowledges that there are other stages but by then the author no longer needs any help.
To all this, Knight has an amusing addendum:
People who start writing late in life often seem to skip stage 1 and sometimes stage 2 as well. I would almost be tempted to recommend that you leave writing alone until you are in your early thirties....
But of course, sometimes the Muse cannot be denied.