I keep learning more about myself (not the pleasant things, of course) because of this sort of introspection. I had absolutely none of it as a kid. I think few people do, but the more you manage -- and the later in life you manage it -- the harder it is to look back at yourself and not wince.
I'd say, and I think the author makes this point as well, at least in passing, one of the hardest things is forgiving yourself when you step back and realize how you've behaved (particularly after condemning others for the same actions). It's a lot easier to take someone else's actions and say "well, he/she didn't mean it" or "OK, that's just how people are" than to look at yourself, know that yes, you did mean it or intend to do it, and no, you don't really find it acceptable.