Dear Stereotypes, why do you exist?

Today, I attended a walk for diabetes. When I arrived, I spotted a student in one of my classes. I waved from afar, and later walked over to carry a conversation with him. The first thing he said was, "I wasn't expecting to see you here." I looked at him with a confused expression and asked what he meant. He looked as if he felt uncomfortable then covered it up by saying, "Well, I wasn't aware you knew ___" (the girl we were walking for).

I was on a website called 'dear blank, please blank' the other day and came across this picture.

We, as humans, often judge people before we get to know them. Before they even speak a word to us, we have already categorized them in our heads. Jock, nerd, punk... So my question is why? What do you think caused so many Americans to be so quick to judge others? Was it how we were raised? Was it the countless movies about high school where the characters are to the extreme?

But I'm not only talking about stereotypes. I'm mainly talking about judging others. I'm not saying this is how everyone is, but what that kid said that to me today made me wonder if I had given off a certain air that made him believe I was someone who I'm not. On the inside, someone may be so very different than what they seem just from their appearance. It makes me sad that someone may not give someone else a chance because of what they physically look like.