Examining a finished work is just torture for an editor. There will always be errors (yes, plural). I’m now styling some of the materials I copyedited. On the one hand, I get to fix what I missed the first time around; on the other hand, I missed stuff. Just so you don’t blow me off with a “that’s because you suck,” here’s an article, written by copyeditors, all about it. Also, this is why we have proofreaders who are separate people from the copyeditors.