How much of the force you are delivering is actually going into your opponent?

If you are tense, then much of it will bang off your attacker's body and back into you.
There is a concussive shockwave that travels along your arm, into your spine and throughout your body.
This is not good for your health.

This is why 4 ounces of pressure is fundamental.
The moment of contact must be heavy, soft and penetrating. Do not push.