Shits happen everywhere

Let me complain about work issues for a bit here. I understand that being a team head has to be responsible for the whole team. But what I don't understand is why some people are really uncapable of what they should be of. Someone keeps asking me about some assignments which he should know about them very well because he's been asking me the same topics for several times already. Sometimes he already knows how he should do but he still asks me. And that kinda annoys me coz he's kinda wasting my time. Tasks and assignments are already rushing and dealing with these people drives me crazy at times. Some people are regulary late at work. I already told them to get to work on time and I'm not the kind of person who likes to repeat myself twice or more than that. We are all grown ups. Why can't they be mature up to their age? It isn't hard to be self-responsible, self organized, and self-disciplined. I hate these kinds of people especially when they are my colleagues. I know that we all make mistakes but sometimes some people just make stupid mistakes repeatedly. Do they know that this kinda act is making themselves untrustworthy? Jeez they're truely useless.