I'll add I was saved from serious head injuries by a bike helmet. Twice. Neither were my fault.

I know someone who wasn't. She had serious concussion. It's not something you want. 2 years off work. Petrochemical engineer - no longer works in the industry because of the injury.

I distinctly remember a kid dying by falling off her bike in the late 80's. She was in the class w/ my younger brother but we didn't really know her. It was obviously a big deal at the school.