This isn't entirely true. It might work in a mild accident with no or just mild injury. When a horse is badly injured or is really trapped in a driving accident, they can't always be harnessed up immediately, and even if they could be, it doesn't always work to 'undo' the accident. They're not really that dumb. I've seen a number of horses over the years that were completely destroyed by a driving accident. They could not be harnessed, they could not be hitched, some of them would start to shake if they just saw a vehicle in the distance. You and an army couldn't safely hitch them up again. It may be different with the lighter training vehicles, but I've seen some that were injured on the track, hitched up right away, and that just did not work. We always had a good supply of ruined horses from the track, in riding schools in upstate NY. They could not be driven any more. And I'm sure they were all handled by trainers who believe what you believe. The problem is it doesn't always work. It's not really quite the same, either, when the accident involves a 1200 lb vehicle and three other horses, there is severe injury, the animal is trapped in the harness/vehicle. Carriage driving horses are very often never able to be driven again after really bad accidents. I've looked at a number of horses in the last 18 months that were for sale cheap because they had been in a bad wreck and could not be driven any more. This is not always because someone is less competent than you. Sometimes rehitching them does not work.