I learn so much from my interns—when I'm teaching them I often find I'm also teaching myself. Recently I asked one of my interns to write up a revision letter on a proposal for a client of mine. Part of the job was an exercise in revision letters and part of the job was to have yet another eye on the material so I could incorporate some of her thoughts in my letter.
After looking at her letter I realized that she made a common mistake for young editors (something I'm positive I was victim of)—she over-edited. I strongly believe it's something all editors do at one point or another. It's not hard and it usually happens when you forget to read the book and let things jump out at you, and instead you read the book with the intent to find things, picky little things.
I think we can all agree that editing and reading are two different things, two different "heads," let's say. And I think there's a place in the middle, a place I call the Middle Editor. It's in between the editor who is looking hard for errors and the reader who avoids seeing the errors so she can just enjoy the story. A good editor finds that central spot (and remembers to go back there when she accidentally leaves) where the enjoyment of the book hasn’t left, but the editor brain is still on. Instead of searching for things to tell the author to fix, she waits for them to jump out at her. There might be many, there might be a few, and, yes, some of them might be picky, but she also learns to enjoy the story as she goes so she can ignore some of those things that are probably personal issues and not real editorial issues.