We are predators. Our forward facing vision is that of the hunter and we fight our best when we can face our target and use our arms. Despite this the hand is a relatively weak weapon. Boxers and MMA fighters need to tape up their hands to protect them even though they also wear gloves. What saves us, primarily, is that the hand is used to attack relatively soft targets: soft tissue in the body and the chin, temple and nose in the head. Because we have neither naturally hard hands or overly long, really heavy limbs the best way to train is to make sure our arms can move fast, in very precise trajectories.
This is where the Fists of Fury workout helps. By practicing to move your arms fast, even when the muscles are tired you are developing strong muscle memory that leads to fast reflexes and helping to develop the kind of muscle density that leads to punching power.