At the center of this book, literally and figuratively, is a compelling idea: a rethinking of the midpoint of a book or film.
In many writing guides, the midpoint is where "something happens." The midpoint, in these guides, never quite reaches the vaunted level of Plot Point 1 or Plot Point 2. Still, something happens at the midpoint. Bell says he's analyzed books and films and has realized that the midpoint is this: a "mirror moment" (not even a whole scene but a moment in a scene) in which the protagonist has to look at herself and decide what kind of person she is (in character-driven stories), or to consider the odds against her.
But more than this, Bell says this is what the story is actually about, its true center. Thus, writing from the middle means that you might wish to first identify this moment, and then you'll know how to get your character there, and will understand your character better, and (in case you missed this) what the story is actually about.
I'm simplifying, but then again, it's a simple--if compelling--concept. As a writer, I think I will find this useful, perhaps even four-stars useful. The book gets three stars, however, because it has the feel of an article stretched to book length (and only barely; it's 92 pages). It's a perfect ebook; three bucks worth of learning. I think I'd feel cheated, however, if I paid ten bucks for the paperback.