I think I developed it because I hit my head in the same place as a teenager - insult to injury. I believe that concussions are accumulative. I do wonder how much the psychological condition of the person has to do with developing it, e.g. if you're depressed or stressed does the concussion exaggerate it? I've also read that people of higher intellect are more prone to it or maybe they just notice it more! I don't think anyone really knows, to most doctors the brain is a mystery.