This is the type of bike my Dad learnt to ride on:
Among their other quirks, they didn’t have a return spring on the throttle (so that you could shoot without slowing down). It also had no rear suspension.
So, my Dad was learning to ride, going around a dirt oval in the Australian bush, wearing rubberised canvas overalls (because leather was thought to be too rebellious for the Army).
Things were going okay until he hit a pothole. That kicked him out of the seat into a handstand above the handlebars. Naturally, his hands involuntarily tightened up a bit, so that when he fell back onto the bike in flying-Superman pose, he accidentally wound the throttle on full.
He was also no longer riding around the oval; he was now charging straight into the bush. And, thanks to the lack of throttle spring, he couldn’t shut it off by just loosening his hand.
He managed to shut it down eventually, but he’d bounced off quite a few trees before that happened. 
