How to break your horse to drive...

Put (half of a) harness on.

Lunge for five minutes.
Hook up to cart.

Apparently this is how these people start a driving horse.

It might have been less of a disaster if the harness had fit. Or been complete. But clearly this horse needed more preparation. And because the harness wasn't complete, the horse was able to repeatedly get itself into trouble.

I hope it took them a long time to repair the cart...