Why are people jerks?

Do you ever sit and wonder why you have to deal with jerks in your life? Like, what is it about people that make them jerks? Is it, they weren't loved as children? Did they get dropped on their heads? Do they just not make enough money? What is it exactly?

I was thinking this today, as I went from phone call to phone call trying to resolve a few issues and having to deal with people that just were...well...jerks. And I thought, gee, there are jerks everywhere in the world. Just think of your last excursion to the mall. There you are clearly in the right for the parking spot with your signal waiting for the person to pull out when someone else zooms right ahead of you and takes the spot. Jerk. Or, there you are in express line at the grocery store with 5 items you're balancing in your arms when the person in front of you has about 20 items. You know because you counted them. Jerk. Or, you're slowing down for the yellow light that you know full well is going to turn red and you safely stop. And, the person behind you starts honking his horn because he wanted to blow the light. Jerk.

I'm sure if you take a moment to think through a typical day, you'll find that you come across many, many jerks. I just can't seem to figure out the motivation for jerks. Do they even know they're being jerks? Or is it accidental? Maybe they're just unhappy people, and should be excused. Unfortunately, sometimes you see the jerks thrilled with themselves for being jerks...which honestly just makes them more jerky, doesn't it?

So, I'm not quite sure what to do with the jerks that I come across in my day to day, other than to try my very best to ignore them. But seriously, if you're reading this and you're a jerk...what exactly is your issue?