Lost my best friend at school to a direct impact on the top of his skull on a garage door at about 10 mph with no helmet on. That was about 20 years ago just as helmets started to come out properly. Never ride without since cracked 2 myself and glad I had them on, strikes me you see more people riding with more armour than less now, saw a group the other day with full body armour on top, lycra below and shin guards for good measure.