This part is much smaller than the contact area of a fist. In this way, the same force and pressure are several times greater. So the attack power is very high. Because of the large contact area, the fist will be greatly resisted by the body. The resistance of the palm stroke will be much smaller, so the so-called penetration is produced. It will cause damage to internal organs. It's like hitting your stomach with your fist. At this time, the abdominal muscles can block most of the strength. If you attack with your palm, it will form a cutting force. Even if the abdominal muscles are strong, they will be badly hurt by this cutting force.