Then, I once sat down to write a story when I was unhappy with the outline. I knew the heroine would defeat the villain by turning his magics against him, but the specific means I chose didn't really resonate. Within the first chapter, the villain owned something, just to demonstrate his wizardliness to the reader, and said something, that added up to a much better solution.
Stories do tend to sprout stuff and develop in the writing. It can incorporate new stuff that pulls it all together. . . if it feels like it.
Not that there isn't a similar problem when you're trying to decide whether you hate the work because it's not ready to go out or you're just tired of revising it.