I have never worn a helmet and nothing has happened to me so far. Even professional bike racers get in serious collisions. I just don't want everybody to see me wearing a helmet. Helmets make it easier for motorists, pedestrians, and other bikers to see you. If everyone can see you, they won't run into you.
Helmets can prevent head injuries-the main cause of death and disability.
A helmet is as much a part of the bicycle as the handlebars and tires.