In "On Writing", Stephen King talks about discovering the story as akin to uncovering a fossil. You brush away a little bit at a time, a little bit at a time, a little bit at a time, not quite knowing what you have until you've unearthed the whole thing. And you shouldn't try to discern what it is until it's all unearthed.
I didn't used to subscribe to this metaphor because I am a plotter. I like to start a story with lots of pre-writing. I spend some time incubating that idea, thinking of neat things I want to include in that story. Then I arrange my neat things in an outline, and use that to guide my first draft. I do not, like Stephen King or Neil Gaiman, start the story with no idea how it ends or where I'm trying to get to. That lends itself to overwriting, in my opinion.
But what I'm learning is that the fossil metaphor still applies. now I'm starting the understand the fossil metaphor, as I go through the first hit of revising. When you are gathering the story ideas, concepts, and neat-things-to-include, you don't have a general idea of how the story goes from beginning to end. Not until you make the outline. This is your first attempt at constructing the dinosaur you have found.
Then you take a closer look at what you've constructed. You realize that you've put some bones in the wrong order. Your bones aren't fastened tightly in the grooves. In your haste to construct the skeleton, you've left some dirt on (this is okay though, as there will always be dirt on a fossil that's been buried so long, and if you take time to meticulously clean every single one, you'll never get it in the museum).
So just because you can see what kind of dinosaur you've got after the first draft, don't let that define what it will always be. This came to me when I was working on Mermaid Story. There's a part in the middle, a low-key section that just wasn't working. Part of it was the order I had put things in when I was making the outline. So I rearranged the scenes and (I think) it's turning out much better. My dinosaur is still the same, but now the ribs don't look so awkwardly placed.
The thing that really bakes my noodle is whether that's because the story was meant to be in that order, or I made it that way. It's still possible to make mistakes when your dinosaur is almost finished. Writers talk about letting the story guide you and other metaphysical bullshit like that. I don't buy into that. I am the author, I control the story. If you let the story control you, it will get out of hand. And then you have Jurassic Park (the park, not the novel).