Sometimes the most difficult thing you can do as an editor is not make a single note - the idea that everything and everyone needs editing is, in reality, a fiction. I've gotten pieces where I thought, Well, I could do this or that, or change this word, but in the end, I leave it. Changing something is not necessarily equivalent to making the piece more true to itself, which is the point of editing: it's just changing it because you feel you can or should or must.