I think a lot of writers will agree that making sure their books are "perfect" is a bit of an obsession.
We obsess over every word, line, paragraph, chapter... you get the point. We'll research something until our fingers are about to fall off from too many internet searches. Our friends will be sick of hearing about a particular troublesome scene and threaten to throw a book at us if we ask them to read it one more time.
Having said all of that, I completely agree with Anne Lamott when she said...
“Perfectionism is the voice of the oppressor, the enemy of the people. It will keep you cramped and insane your whole life.”
All that obsessing over how we write our books or scenes can really kill a story. When you over think while writing, you second-guess your decisions, which leads to endlessly rewriting particular scenes, changing whole passages to try it another way, or scrapping the whole project.
Now, yes, sometimes these things have to be done, but not every time you sit down to write. If this is your process, it'll be awfully hard to ever finish a book or story. Every writer has to develop their own process, but here are a few tips I've picked up over the years.
Tip #1: Whether you like to outline or not, don't limit yourself to sticking to your outline or notes verbatim. If you feel like the story needs to take a left instead of a right, or a U-turn in a whole new direction, go with it. Let your plot develop organically and don't feel like you have to go back to an outline and re-outline after every change. Just write.
Tip #2: Don't edit while you write. You'll kill your progress if you go back and edit what you've just written. Give yourself some time to let that chapter or scene sit and solidify. Even if you have to reread a chapter or two when you come back so you know where you left off, DON'T EDIT, aside from maybe a few typos. Even when you finish the entire book, don't jump right into editing. Work on something else. Give it at least a week (longer if you can) and come back to it when you have fresh eyes.
Tip #3: Sending your work out to beta readers (readers who read an early draft in order to give you feedback and suggestions) can be anxiety laden. It always is. Waiting to send it out until your book is perfectly edited and all the holes are filled in just isn't reasonable. Find beta readers you trust to be honest, let them know it's not a perfect story and you need helpful critiques, and hit the send button. There are always problems with a manuscript that you as the author won't be able to see. Waiting until it's perfect just prolongs the inevitable and often leaves you with more revisions to make than you would have had otherwise.
Tip #4: Give yourself permission to make mistakes. Don't want to put a scene on hold to do a little research? Not sure if what you're writing is possible, but the scene is just begging to be written? Great! Keep writing! You can always go back and correct mistakes. In fact, you usually learn a lot from making those mistakes, and then you don't make them as often in the future. It's tough to get into a writing groove sometimes, and if you're in one, let yourself just get your ideas down on paper and worry about refining later on.
Tip #5: Accept the fact that your book will never be perfect. That's just how it is. There will always be something you think could have been better, or should have been changed. Reviews will make you doubt scenes or chapters or endings. It will never, ever be completely perfect...and that's okay.