In school, I was told a rule of thumb which I try to live by:

95% of everything you write is crap.

Which is a brutal way of saying that rewrites and re-evaluation are always necessary. However, it's not always possible to objectively identify problem areas. Sometimes an outside opinion is necessary.

So long as you do me the favor of pointing out what works and what is good, as well as what's bad, there shouldn't be a problem. It's easy to forget that, but I'd like to know what is working just as much as I need to know what isn't.