I have a theory that a story should be condensible to a perfectly logical few pages. At its most brief telling-- the way you would tell someone who might be interested in buying the book, for instance-- If someone asks "what is your story about?" You should not say, "I don't know." I mean, there is a certain level of credibility you need to be a published writer. It is a professional field. In many cases you have to defend your decisions, and you can't if you have no idea what you are doing. You should be able to write a brief one page synopsis of the story-- every sailent feature intact. At this stage, you should see the entire story from a eagle's eye point of view. You're thinking of being on the ground in the bushes, so to speak. You need to rise to a height where you can see the entire story in a panorama...
I call this the "campfire version," but it can be also a kind of fairy tale.
My guess is if you cannot recite this shortened version, of if the logic breaks apart at this stage, then you have a flawed story that needs fixing before it is considered "done."
All but the most experimental of stories have an internal logic to them-- Just a rambling diary like bit of writing will not transform into a story unless you know what the logic is.
I really don't imagine that anyone who writes just writes without remembering what they have written, and how it fits in with the logic of the story.
Now what happens if you are published, and someone wants to interview you about your book. I can imagine it: "Tell me about your new book," asks the correspondent. "I really don't concern myself with what I write," you say, "in fact, I forget what I write as soon as I write it. I just put it in a box and ship it to the publisher and pray that it makes sence."
Tisk. Tisk.