I got hit in the mouth with a golf club when I was in 4th grade. Knocked out three teeth and had a concussion to boot. My mom said it changed me. When I asked her why she said this: It made you self-conscious, not only about how your mouth looked, but your body image in general. I think you became less out-going, less talkative. You saw first-hand how people's actions are unpredictable, so you were not very trusting. You displayed feelings of pessimism, maybe even a bit of paranoia, and started being sarcastic. You no longer had the self-confidence that you previously had: not socially nor scholastically.