It takes courage to face an opponent with a receptive heart and a willingness to accept, to yield, to be sensitive, and to be decisive.
Faith is necessary.

A student may fail many times before they have the heart to do what they have been told to do.

When thinking stops, the art begins.
Self-consciousness and though are impediments to the way.

Internal kung fu cannot be approached like karate or judo.
It is simply not the same thing.

Sure, commonalities exist.
But so much differs.

Tai chi and baguazhang are infused with taoist insights and discoveries.
But only the earnest student succeeds in this regard.
The lazy person uses force, or ignores the precepts of the art, bastardising it to suit their own lack of faith.

Having completed a puzzle, you may understand how the pieces all fit together and why.
Some of your breakthroughs occurred through methodical reasoning.
Others were intuition, and cannot be rationalised.

Mistakes can also lead to understand.
It can be useful to know what does not work.

When Sun Tzu speaks of invisibility, he is speaking about moving without attracting the attention of your opponent:

1. Concealment
2. Covert
3. Disguise
4. Espionage
5. Hidden
6. Misdirection
7. Secrecy
8. Stealth

Sun Tzu wrote a whole section on spying.
From a self defence perspective this is very useful.
You do not need to become a spy, but you can learn how to avoid being noticed.