I've cracked my skull many times throughout my life off the bike. Doesn't take much force to cause issues. So I don't ride without a helmet. Ever. I've also had enough spills now on the bike where I've smacked my head but was completely fine. One time I was going real slow up a hill but hit a thin sheet of ice. Rear wheel went out from under me and I fell back. First thing to hit was my head. Was ok and went home without a scratch. Without a helmet I would of been in a world of hurt and possibly knocked out. At the least I would of been bleeding and extremely disoriented. Instead I was able to get my wits back in an instant and look for other road users to register my danger. I don't tell others what to wear, but I know and hate the feeling of hard impacts on my skull. My helmet has saved my noggin several times. Not everyone needs to. Hell if you at going 10 mph on a trail out of traffic I completely understand. But for me no matter where, or how fast I wear one.