Surnames

What is it with surnames? Or last names, for those of you who don't know what a surname is. My friend once asked me why people sometimes call each other by their last names. At first, I thought, he was just being overly inquisitive like he sometimes is, but then I started thinking about it, and I can't see one good reason why they do. It adds no specification, like you first name might. It's only there to indicate what family you belong to. And it doesn't even do that sometimes, because there are a lot of people with the last names Smith and Johnson. I wanted so desperately to prove to him a reason for people to call others by their surnames, but it is not possible to me. I can see absolutely no reason.
Well, that was a good rant. I certainly think so.
Semester finals were today. I had to tests, one of which was excruciatingly long, and I had to write about three pages worth of things I learned in health. On the bright side, we watched the Karate Kid in Chinese.
That's right, I'm taking Chinese. I could prove it to you in real life, but not on here because I could easily just look it up on Google translate.
I am finished. Here is your picture.