You come around a corner, heading toward an intersection. You don't have a stop sign, but the other street does. A car pulls up to the sign and stops. You think the driver saw you, and you take your eyes off of that car.
We know that helmets save lives. If you talk to safety experts about motorcyclists and traditional cyclists, they'll tell you that every single one should have a helmet on. They'll tell you that it doesn't matter what the law says -- many states do not require helmets -- because the evidence shows that helmets increase safety, decrease death rates and a lower brain injury rate.