I once was an avid cyclist and always wore a helmet. On one ride a friend of mine was no wearing a helmet and someone came up to him (not from our group) and said to him, "They can fix everything except the brain".
I've actually collided with a car. Went right over the hood and the top of my helmet skidded three feet across the hood of the car that cut me off. The driver was exiting a parking lot driveway and failed to yield. I had a hairline fracture of the wrist and minor scrapes all over. I did in fact walk my damaged bike home. However - my head was just fine and my helmet was properly fastened. I see too many people who wear their helmets loose or way too high; they should cover most of the forehead. When they're loose they can expose part of the head on impact.
I remember hearing that a simple unobstructed fall on a hard surface just three feet onto the head could be fatal. Most of us don't worry too much about walking or running, but riding a bicycle (or rollerblading at high speeds) can mean sudden circumstances where loss of control could mean landing direct on a hard surface (car, window, pole, tree, pavement) with far more energy than that simple 3 ft fall.
