Second rule is that nobody will have a video camera running and the rollee will decline, with feeling, any attempt at a re-shoot.
The ones I've seen had two common factors. One incident resulted in an attempt to climb a 45 degree grass bank, the other from a misguided attempt to ride a Trice Q on one wheel and the rear rack. OK he was trying for two wheels but the rack intervened, this is a little known property of ICE racks.
The factors were:-
1. The rollee was being an idiot.
2. The rollee had taken drink shortly before the incident.
There is a third factor. The witnesses first reaction (Perhaps linked to both items.) is to roll around laughing, spluttering and generally making the rollee as embarrassed as they can, and then make multiple requests for a repeat performance. This occurs long before they enquire about the health or otherwise of the lunatic rollee, or more importantly the rolled trike. In both cases I have seen, which happened within 20 minutes of each other, the audience were also riding trikes and had also taken a small sherry... or three. Well maybe not sherry, unless the pub serves it in pint glasses, and maybe it had been slightly more than three in some cases.