My kids have never disappointed me. Maybe it's just a matter of semantics? I'm not sure. DS1 has done a few things I didn't like over the years -not many, but a few - but I've never been disappointed, as such. We talked over the things he did wrong, and applied consequences, as necessary. But, I see childhood/adolescense (well, all of life, but those times, in particular) as a time of learning. When my child does something that I really don't like, I just see it as a lesson that hasn't "taken" yet, not as something to be disappointed by.
The worst ever was probably when ds1 hit a girl in our complex when he was 12...totally out of character for him, and quite a shock. He talked to me about it, went up and down about how to handle it, felt like crap, etc. He eventually went and talked to her and apologized for what happened. He's never hit anyone since. I wasn't happy that he hit someone - not happy at all. But, it never occurred to me to be "disappointed". He's only human and he was only 12 (I remember all too well what those hormone storms can be like!), and he simply found himself dealing with a situation that he lacked the coping skills for.
We have constant and recurring problems with ds2 and hitting. I'm frustrated, exhausted, and bewildered...but not disappointed. I just don't know what's going on in his head, or how to get a handle on it. Honestly, if anyone should be disappointed, it's probably ds2 - I'm the adult, and I don't know how to cope with it.
I'm rambling (I do that). I just see my kids as both separate individuals and "works in progress". I'm not disappointed by their slip-ups and mistakes. We all make them, and I don't expect them to be an exception to that. DS1 is almost grown. There are areas where he deviates from my hypothetical "ideal" (he's a real mooch, for one thing!), but he's...ds1. He's not me. He doesn't have to have the exact same standards of conduct, yk?