It’s one thing to reach the final sentence of a first draft. It’s quite another to be able to sit down and read your work through—without stopping. The work of creating a first draft is very hard, often grinding. Constant rethinking. Constant rewriting. Changes can be big, even as there are countless small ones.
But the decisive moment, I think, is your ability to sit down and read your work right through. I hasten to add that even if you can do it—without rushing back, horrified, to your keyboard—your work is not done. But at least you have a consistent flow, a sense of a whole, and view, if you will, of the entire landscape. After all, a novel is more than the sum of its parts. If you think of the novel as a jigsaw puzzle, whereas there can be many beautiful pieces (or moments), it is the image as a whole that brings you to another place, a summation, or revelation, if you will, of something big. That is the great achievement of a good novel, and its greatest challenge.