Having a child run out in front of me. They're so small, they can appear from out of seemingly nowhere. I talked to a guy before that had hit a child with his bike. He was absolutely destroyed by it, even teared up talking about it after something like 15 years. The child didn't even die, went on to make a full recovery from a broken leg and some serious head trauma. He described watching the small body skid down the road in front of him as the single most horrifying thing he had ever witnessed. Hasn't rode since. He hadn't become anti-motorcycle or anything like that, just said that there was as much chance in hitting someone with his car, but that he was much more cautious in a car and trusted the brakes better.