You have to work out your whole being, it's not one aspect of yourself that you are training, it is your very nervous system that is being trained. Forged, heat treated, carved from a block of wood. Removing the inessential aspects of yourself, a sculptor doesn't add, he subtracts until the final shape is revealed. Your fine motor control is only possible because your nervous system is pruning all the unnecessary neural connections to your muscle fibers. A small child hasn't had this neural pruning, they're clumsy you wouldn't trust them with a bench grinder.