This afternoon, I got a new ski helmet for my birthday. In most high speed accidents, helmets can't do much to keep you safe. At high speeds, it's the blunt force trauma that can kill you. But the most common skiing accidents are not the high speed accidents, they are the on-slope collision accidents. Like driving down the highway, the greatest danger in skiing comes not from your own errors but from the mistakes of other people on the slope, as this video shows.
That's why the obsessive skier wears a helmet.