There's this thing that kinda annoys me. Often there are people who don't feel like talking or paying attention in certain situations i.e. they don't give a fuck. Sure, the reason for that can be lack of self-confidence or whatever, but it seems that almost always the latter is assumed. Like, me personally, I'm very talkative with certain people but I don't want to talk in some other social situations, and there are some people who take me for this shy dude, and it's like they don't even consider the option of me not liking to talk with them.
But it's not a personal thing as much as it is a general observation. I've seen plenty of teachers defining the quiet students as not confident whereas I know that many of my peers have simply not been interested. I also often withhold speaking in class because I don't think it's worth my effort rather than being "afraid" to speak.