This is where many get frustrated. The point of writing a great deal of material, quickly, in a first draft, is to get it down on paper, so that you know what you’re writing about and can shape your book in subsequent drafts. First drafts are where you see what you have, if your characters and ideas have the stamina to make it through a novel. If it’s not on paper, it can’t be shaped and molded into something better. If you wait until you’ve written the perfect sentence in your head, you won’t write.
There are times when you figure out you need to go down a different route. That’s fine. But don’t go back and rewrite what you’ve done up until now. You need to move forward.
What you can do is to go back and mark, in a different color, what I call “placeholders” – notes where you want to make changes in the next draft. And then continue from your stopping point with the new direction.
If you keep going back to revise, you won’t finish. I believe that it’s detrimental to revise until you have an entire first draft, because you need to get the big picture before you can focus on the details. In subsequent drafts, you can work on each chapter as much as you want before moving on; you can flow back and forth. But in first drafts, keep moving forward.
In my experience as a writer, a Trusted Reader, a mentor, a teacher, and a critiquer, 97% of the people who keep going back to revise and claim it’s because they’re “perfectionists” are really afraid of finishing. Because if they ever finish, they have to take the next steps, and someone might reject them. Fear of failure keeps them from finishing, but they pretend (often even to themselves) that it’s because they’re perfectionists.
Perfection is for final drafts, not first drafts. You won’t reach perfection until you have a draft on paper to perfect.