First comes the wild idea. It grows gradually in your creative self, until it feels like an elephant in the corner of a room, not letting you ignore it. Until you're compelled to get it on paper.
You write for months or years. You now have a huge file on your hard drive or piled on your desk. You rework it, get feedback, rework some more. Hate it, love it, feel neutral.
Finally, you're ready for revision. Revision is essential; we know that professionals spend most of their book journey on this final stage. But if it's our first book, how do we figure out what needs attention? It reads OK, our writers' group loves it. But we still sense the book isn't ready to go out to agent or editor.
Without a plan, a map, revision can feel endless.