The risk-reward ratio for mountain biking is substantial when compared to skiing and snowboarding. You can certainly get injured or die doing winter sports, but you’re more likely to get cut up, bruised, or break a bone while riding a mountain bike due to the solid, non slick ground you’re riding on.
I think every skier should wear a helmet, and I believe every mountain biker should have to wear a helmet.
Supporting video #1:
