Magic beyond the plan

I can plan a book as much as I like—write detailed outlines, scene lists, synopses; I can map and collage and color-code as much as I like, but the actual story happens when I sit down, open the window into that other world, and let the characters go, do their thing. It is only in sitting down, day after day, that I discover that one character, a taciturn ex-soldier, really loves cats, and shows another character a secret about barn cats that has some very strong metaphorical underpinnings for the girl’s journey. I couldn’t plan that, because I didn’t know it. It’s only in the writing, only when a character takes a sudden turn into a new action that surprises me, that I learn who she really is beneath her Paper Doll Place Holderness. -- Writer Unboxed: Day After Day After Day by Barbara O'Neal

And this why I don't understand when writers say they can't plan a story because that takes all the fun of discovery out. You still get this no matter how much you plan!