I was a theatre director in a former life and I've also been an editor. Directing has a lot of similarities with editing written works, it turns out.
I say 'it turns out' because I've just realized the most important similarity, and not because I was editing anything -- my work was being edited. A first for me in a very long time.
When you're directing, you are watching, observing, absorbing all the time. Actors work in different ways, at different speeds. At any given day in most of the rehearsal process, the members of the cast will be at differing stages of progress.
Part of what you do as a director is to work to keep everyone moving along together. It's never entirely possible, but it's important to try. The actors play off each other; they learn more about the other characters and their work becomes richer, more nuanced, more alive.
One of the ways the director helps this process is to spot new ideas -- an actor starts to explore something new. If it's got merit, the director can encourage the actor to take it further. Of course, the reverse is true as well. The director is sort of artist, critic, coach, and audience rolled into one.
I am working with an editor I have never met, but he has the insights of a theatre director, but in literary form: he's a writer, critic, coach, and reader. Like all directors, he understands form and shape and pacing. But this editor, like a good director, also puts his finger unerringly on moments not fully explored, on ideas to develop further, on making the interplay between plot and character more alive.
How great is that?