"How do I know what I think until I see what I say?"

I feel like there are many ways to interpret this quote. I think about writing when I read this. Many times when I write, I don't concretely know where I'm going with it until I am in the process of writing it. That is when everything comes together for me. Of course it's entirely possible that the word "see" isn't supposed to be taken literally.
As to the story, "Where are you going, where have you been?", I thought it was odd. Since the theme of this course is retellings I can completely understand why this was chosen for us to read. It's like deja vu almost. You know what's going to happen though it's never actually happened to you before. The intro, long as it was comparatively, threw me off though. I had no idea how it was relevant or where it was going until Arnold Friend showed up at her door. I suppose it was written that way to give us some idea of how the girl might react to this situation or just to provide more depth for the character.