You press the thumb against the index finger.
Pulling the thumb back toward the wrist is just retarded.
Do you see guys doing a phoenix-eye fist without a thumb brace? No, you don't.
Doing it without a thumb brace is a good way to **** up your knuckle AND your wrist.
CLF schools that teach a panther fist without a thumb brace should be ashamed they are teaching students a good way to ruin their fist/fingers/wrist/hand.
It is bias to think that the art of war is just for killing people. It is not to kill people, it is to kill evil. It is a strategem to give life to many people by killing the evil of one person.
- Yagyū Munenori