wingedbeast

Competence is a good way to look at it. Another way to look at it is depth. Sokka, for example, for all that he's a huge goofball, has layers - things he's serious about, things he worries about, responsibilities he feels. We can connect to him as a person, not just a context-less stream of wacky antics, and it's that personal connection that makes the antics endearing and not annoying.