Little kids can bounce back from almost anything. They'll crash bikes into walls or run into goal posts and pop up feeling fine. During a game of Capture the Flag at summer camp one year, an 8th grader was running full tilt with a flag and looking over his shoulder at his pursuers. A baseball backstop right in the middle of the poorly designed Capture the Flag course caught up with him, and he ran into at full sprint with his head turned. He broke his arm and knocked out three teeth. Once you hit a certain height and body size you can't bounce back from those accidents like really little kids do. A dangerous lag in human development exists between when your body is big enough to get hurt and when your brain knows you shouldn't be running as fast as you can with your head turned around.