Leg problems are far less likely in a mule than in a horse, and when leg problems do occur, they are far less severe. Mules live longer productive lives than horses do. Farm mules average 18 years to a horse's 15 years. Mules can more easily than horses be handled in large groups. Mules can be corraled on farms 30 or 40 to a group, or up to 500 in a feeding pen, without the injuries or other consequences commonly seen with horses.
Mules have a strong sense of self preservation.
This is one good reason why mules physically last longer than horses do. If they are overheated, overworked, or overused for any reason, mules will either slow down to a safe pace or stop completely. Mules are not stubborn. Neither are donkeys. The facts that mules are inclined not to panic, that they think about what is happening to them, and they take care of their own physical well being prevents many accidents that might happen if they were horses.