The Art of War

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.