I never do a full outline, and if I did, I would not feel bound to it, because the view from inside a scene can be different from the view outside it. But neither do I just start writing and see what happens; I am far more disciplined than that. ↗
I did not know at first that it would be a series; I discovered after the first novel that I had more to say about it, so I did another. And another, and then the readers demanded yet more. ↗
You can think you've made it and yet the next day's press will always be waiting for you, the public will always ask more of you. In short, you can always do better! ↗