I can't prove that a helmet has ever saved me from a head injury, but over decades of cycling, a helmet has saved me from pain several times. This is not a thread about whether helmets save lives, or whether helmet laws are a good or bad idea. It's a thread about pain and the lack thereof.
About fifteen years ago, I was stupidly and quickly riding a MTB across a parking lot at dusk without a headlight (again, stupid, stupid, stupid). I didn't notice the metal cable going across the driveway. WHAMMM!. The cable hit me in the chest and I went flat on my back. My helmet hit the ground hard, but I felt no pain on my head. By contrast, I had a nasty bruise on my chest for a long, long time.
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