For my money, the best advice in this book was, "let me urge that you take your story through at least two drafts; the one you do with the study door closed and the one you do with it open." (Emphasis mine.)
Writing a book is a funny thing: you're basically inviting the public to take a guided romp through your heart. And even though I (rarely) think when I read someone else's book, "what kind of person does it take to entertain thoughts like these?" it's very hard for me not to expect people to wonder that about me.
I mean, the truth is that everyone thinks about God, sex, and death, about survival and love and pain, so your average author isn't really going into unexplored territory, humanly speaking. But most of us don't tell each other what we think about all those primal things, and as authors we don't tell you what we think exactly, but you know that in order to write characters whose experience encompasses all of that we have to have thought about it, and thought about it a lot and thought about it hard.
Which feels embarrassing, even though it isn't.
So in order to keep that embarrassment from hindering you in writing something that really says something about life, the universe, and everything, it makes sense to keep your work private, at least the first time through.
Of course, if you never show it to anyone and write like you never intend to show it to anyone, it'll just be heart-barf. Blaaaaaargh. All your id and super-ego and angst, vomited out there on the page. No one wants to see that. But I don't think that's what King is suggesting.
After all, here is what he continues on to say:
"Here's something else - if no one says to you, 'Oh Sam (or Amy)! This is wonderful!," you are a lot less apt to slack off or to start concentrating on the wrong thing . . . being wonderful, for instance, instead of telling the goddam story."
Yep. Really, the whole point is to stop looking at yourself and to do the work. Anything that aids that goal is to be embraced, whether it keeps you from being embarrassed or keeps you from preening.
Do the work. And I think that might sum up the theme of this very admirable book.
Read it; it's good. (Standard disclaimers for adult content and - as is obvious from the above quotation - language apply.)
Peace of Christ to you,