Helmets are good. Not only does wearing one (gasp!) protect your head from severe injury, but it can even protect other people's heads from severe injury. (By modeling good behavior and convincing them to wear helmets...)
I was recently trying to explain this to Mr. Skateboard. Between multiple traumatic brain injuries and organic brain damage from before he got sober, Mr. Skateboard's memory is somewhat impaired. (He didn't come see us for three months because he forgot where our office was.)
"Are you wearing a helmet when you're out skateboarding with the kids? Because a bonk on the head can really scramble your brains," I said.
"Nah, I been bonked on the head a lot and I'm fine!"