Why is the fist hard?

Factor 1: acting force. The role of the human body is not the ideal confrontation of junior high school physics. The intricate direction and focus of the force will affect the effect.

Factor 2: The endurance of human tissues is different. It can be improved by exercise.

Factor 3: The neural perception system varies from person to person.

It doesn't matter if the delicate sensory nerve of the fist is destroyed. Professional boxers and people who specialize in training hand hardness. Calluses accumulated by hands due to perennial exercise form hard tissue higher than that of ordinary people, and they will not be conscious when knocking on stones.

If you are below 16, it may affect the development of bones.