When I was much younger, I thought that books appeared, fully-formed, in an author's head, and made it on to the page in much the same way: the writer would begin with the title, then the first line of chapter one, and then continue writing until the story was done. Like I said, much younger.
As I thought about the craft of writing more, I allowed for the possibility of drafts. But even then, the idea I had in my head of what went on in revising a draft was much like the kind of revisions I did on essays for school. The addition of a new paragraph, perhaps, but generally just tweaking the phrasing and word choices to be more felicitous. After all, these were Professional Writers. They would certainly know what they were doing.
I couldn't even type that last sentence with a straight face.
Maybe there are writers out there who begin with an outline, who have a cast of characters, and a list of scenes before they start writing. And maybe those characters and scenes remain the same on the page as they were in that writer's head.
I am not that writer. Not even close. I usually start with an image. An angel, terrible and beautiful, with her head in her hands, weeping. Sometimes with a first line. "He wrote me into a story again." This novel? Started life as a short story, written in a mad three days without sleep, and was a response to a challenge, and a quote from Hamlet: "I could be bounded in a nutshell and count myself a king of infinite space, were it not that I have bad dreams." I didn't know the end when I started. I usually consider myself lucky to know the next line.
But today I do know the end. A battle-scarred young woman, sword in hand, walking out of a labyrinth, white wolfhound at her side, into the sun and melting snow. There are three scenes between here and there.