So, back in Tucumcari (New Mexico) in the '70's, I had the three wild 3 year old horses that had never seen a human being until being herded into a stock trailer and delivered into the aisle of my barn! Leon, Billy and I worked with them slowly and with clear, consistent methods that we developed as we went along.
Dawn was a very timid mare, lovely and curious but quick to react and to flee. We were blessed with a huge aisle in the barn (I could ride in it - the ride-able ones among the other 15 horses we had at that time) and there was a translucent garage type door at each end. Leon was preparing to work with Dawn one morning, teaching her to lead. He would start with her in the 14 x 14 stall and patiently take her into the aisle, then back to the security of her stall, a little farther out into the aisle, then back... he'd been working with her like this for around 10 days.
This particular day I reminded him to wear a helmet (we called them hard hats back then!). I was in a stall, mucking while it's occupant was turned out and I saw Leon taking Dawn pretty far down the aisle with all going quite well. Our barn was situated so that vehicles coming down Highway 19 from the south would look right at the end of the building. In a flash, something triggered the filly and she bolted - Leon had her head pulled toward his body trying to stop her and she was zooming toward the closed door at the end of the aisle. Her "binocular" vision was non-functioning, her peripheral vision couldn't see what was ahead of them and the two of them exploded out through the door, pieces flying in all directions! Leon still had hold of her! She was momentarily stunned and he was able to turn her and lead her back to the barn quickly. AND, neither of them were harmed! The door was totaled - but I figured, if it had been sturdier, they might have even been killed.
Later, I wondered; if anyone was driving casually down the highway, around the turn to face the barn, watching the scenery, just as the door exploded into a thousand pieces and a horse dragging a man burst forth from the opening - what must they have thought!