From a humorous interview (an aside: when no one is able to make a decent interview, writers have to interview each other to compensate):
As you’re probably well aware, editors in the book world often do a lot of the work for a fraction of the glory, and tend to serve as scapegoats for the wrath of readers. If people like a book – well written. If they hate it – badly edited. And the odd thing is that it’s virtually impossible to tell from the finished product how good the editing is, as you’ve no idea what state it started in.