I had a cycling accident where I misjudged how tight a corner was, ran off the path, high sided and head planted into a tree. I wasn't going fast, maybe 10mph, but clearly too fast for the corner. First injury in over 15 years of cycling. Nobody else involved, indeed, nobody else in earshot, let alone cars.

My friend was cycling up a hill on a cycle route and his handlebars fell apart. Not sure why, think it was metal fatigue - they split down the fork. He woke up on the floor with his helmet in tens of pieces and with no idea what happened.

Things can just go wrong quickly on two wheels, and the outcome is often smashing your head on something.