Softness and yielding are yin qualities. They require physical sensitivity and awareness.
Instead of pushing, you must yield into the opponent.
This is accomplished by allowing your body weight to move.

Pushing hands is an exercise in yielding; you relax your own body enough to allow the opponents force to move you and then you shift your weight in order to move them.

Should your partner present more than 4 ounces of resistance during the exercise, you must stop pushing immediately.
Once you learn not to push against solidity, your physical tension will start to fade and your body will begin to use gravity creatively.

'Reasonable force' requires you to be cautious in how you treat an attacker.
Do not make it an emotional event.

Be practical and expedient.

Your aim is to incapacitate temporarily. It is not to exact justice or vengeance.