Yep. And it's really hard to figure out when you're confusing for the reader, boring, your pacing is off, etc. (At least for me.) A good editor/beta can not only point out stuff like that to you, but can also find ways of potentially fixing it. (i.e. Mary was boring, but I think she was because we never got a feeling as to why she agreed to go on the epic quest...)

The challenge is in finding the good editors. ;) But they're around if you hang out in a critique group long enough and offer enough of your own critiques!