Curious if you have ever fallen off a bike? I have fallen over several times on a bike while stationary (when learning to ride with clipless pedals), I have crashed bikes at much higher speeds as well, and I have watched my kids fall off of bikes lots of times while learning. In all of that, I have never seen a (or had my own) head hit the ground. Typically you hit the ground with your arms (slow speed or stationary fall) or your hips, back, or shoulders (if at higher speed).