Like Leaning Right said, situational awareness is rule #1. Like sun Tzu said, know yourself and know your enemy. That is what situational awareness is at its most basic level. Example: if I’m walking across a dark empty parking lot and I observe individuals approaching me. I am going to become responsive well before they get within 21 feet. I’m going to prepare to defend myself. The shirt or coat concealing my firearm is going to be moved out of the way. My hand is going on the firearm. and I’m going to maneuver to disrupt their plan of attack, to keep them more than 21 feet away from me, and to force them to reveal their ill intent outside of 21 feet. The situation would be much different in broad daylight with witnesses all over the place.
We think alike. I held training sessions with my wife to demonstrate that what she thought were safe distances were actually danger zones. Then we drilled on methods to increase/maintain distances under different situations and getting control of her weapon before someone closed with her. It has increased her situational awareness a lot. We have also held scenarios about what to do if SHTF and we get surprised by a home invasion and one is armed while the other is being used as a shield by the invaders.