I never dreamt I could be an author when I grew up. It just didn't occur to me, because I thought you had to be a) academic, so go to university, things like that, and I didn't think I was clever, or b) dead because I just assumed all the authors in the library were dead.
I simply don't understand authors that know everything before they write it; it seems so cold blooded. I think it's lovely when the story takes over and goes somewhere else.