It's true, one very rarely meets people who have suffered serious head injuries without a helmet. You will never talk to a cyclist with that kind of serious st

It's true, one very rarely meets people who have suffered serious head injuries without a helmet. You will never talk to a cyclist with that kind of serious story. It's a sampling problem: you only talk to cyclists. The head-injury cases who didn't wear helmets are injured or dead, and correspondingly no longer cyclists.