Is that something common at Hacker News? I find it worrisome that someone can be banned from a community and not even be aware of it. What's the point of punis

Is that something common at Hacker News? I find it worrisome that someone can be banned from a community and not even be aware of it. What's the point of punishing wrong behavior if the one making it isn't aware that it was wrong? I'm trying to grasp how moderation and banning works around here, but it's difficult since neither the FAQ nor the posting guidelines have an explanation about it.