As in most aspects of life, so it is in story revision: Fixing the problem is easy. It's finding the problem that's hard.

Repairing a flawed story is usually relatively simple; often a matter of changing only a few lines or paragraphs. The challenge lies in deciphering ambiguous and often contradictory feedback in order to determine what the problem actually is. I have seen stories murdered in revision by authors struggling to address random symptoms rather than searching for the as-yet-unidentified underlying problem.

This, I think, is why a good editor is worth his or her weight in gold. I've heard people claim that editors edit because they can't write. I don't think this is true. Or rather, I think it is irrelevant. Editing -- that precious skill of being able to sift through pages of prose and spot the one key flaw that is causing all the others -- is a very different skill from the ability to paint a story with words. Most writers train both skills over time, but there's no rule that says they must necessarily both be present in the same person. A good editor may also be a good writer. Or he may be a lousy writer. But an editor's writing ability says, in my opinion, absolutely nothing about how good he or she is at editing.