Bad guys always have the initiative. Defenders are always reacting. This is core to our laws, and our social contract with each other.
A teacher demonstrated how this relationship affects a defender's response time.
He had me point a finger gun at his head. My job was to say "Bang!" when I saw him raise his finger gun from his side and "fire" at me.
I knew his "attack" was coming. I was watching his hands carefully. Yet, every time, because he had the initiative, he could raise his finger gun and "fire" at me before I could see his hands move, process what I saw, and decide to say "Bang!"
Try this with a friend. You'll experience "initiative deficit" firsthand.
Lessons:
1) No amount of "situational awareness" can overcome this "initiative deficit."
2) Initiative deficit is one reason why cops are trained to exert "control" (to maintain the initiative) as much as possible. (Soldiers and fighter pilots, too). And why domestic violence calls (where this is difficult) are so dangerous for them.
3) Defenders practice hard to get from a "Go!" decision to an on-target "Bang" as quickly as possible. So that when an attacker yields the initiative, even for just an instant, the defender can overcome his ever-present initiative deficit and prevail in an armed attack.
Watch an example of this principle here:
4) The initiative deficit, combined with time to first shot, is the basis for Tueller's so-called "21-foot rule".
5) Simulators, videos, and real field experience help defenders get from observed bad guy behavior to a "GO!" decision more quickly, but cannot eliminate the advantage of having the initiative.