Making the pieces fit: A living city and a dog

I think I've written in a previous post that I'm the kind of writer who likes to bounce a story in my head for quite some time before I seriously tackle a first draft. I'm a big believer in symmetry; the mind responds to it unconsciously, and if it's provided in the natural progression of the work then hopefully the reader goes away feeling satisfied rather than manipulated. The problem with this approach is that knots often appear in the plot that have to be teased out before it will work. This usually means (and I'm speaking only for myself here) that a character is missing. If I were a cynical Word-God I could simply spin one up out of clay, give it a name, and blast it into life. But I don't have those divine powers. I'm more of a revealer, I think, than a creator. This often means I have to wait, and search, until I can discover who or what is missing from the constantly changing pages in my mind. They usually come to me when I'm not thinking about them too hard- sometimes I've merely misplaced them in another half finished story or half realized idea, and sometimes they're hidden within the contested piece itself, but when I finally find them and put them in their proper place it's like a fog lifting and a clear straight road for miles, no curves in sight.