As a good rider and partner for your horse, you want to work with your horse in ways to ensure an emergency stop or dismount is never required – because a runaway situation is never triggered in the first place. Instead, your training and partnership with your horse means you help your horse stay calm, and you recognize when he’s getting stressed before he becomes overwhelmed.
Bolting, spooking, and bucking are defensive behaviours designed for escaping and fleeing from danger. The horse will stop when he feels he is at a safe distance between himself and that perceived threat.
On a trail ride, your horse might startle and bolt when a wild turkey runs out in front of or behind you, for example. If your response is to become tense and pull back hard on the reins, that adds more fuel to the fire. Your horse’s stress increase, and he keeps running from that pressure.