You've ventured onto a piece of ground that we need to tiptoe around...the overwhelming problem here is that the need for training often gets shunted aside in the face of more immediate needs. If you are going to carry a gun for personal defense, or if you keep a gun in your home for defense, you have a need for training. That is the reality of the situation. Furthermore, the skills are perishable. We emphasize that over and over on the shows.
Your level of training dictates whether you will be an "aware sheep" or, indeed, a "sheep dog," to bastardize the Grossman terminology. An aware sheep is QUANTUMS better than the pathetic hordes who think they'll be protected by the police, by the government, by...I don't know...aliens. On THE BEST DEFENSE we've shown scenarios where the situation went south because the good guy drew a gun and escalated the situation. We've also shown scenarios where the good guy hesitated and because of that hesitation lost his life.
I've "died" a lot of times in "simple" convenience store robbery sims...all violent encounters are pure chaos systems, beyond prediction. Whether you live or die depends not just on your training but your mental flexibility, the ability to move from plan to plan to plan in fractions of a second. I believe that is a function of training. When I was training as a cave diver, my instructor hammered into my head over and over that the techniques I was learning, while basically simple, would have to be performed in just about the most terrifying claustrophobic environment a monkey which evolved from trees and plains could imagine — a coffin-sized pitch-black underwater cave, with the added incentive of running out of air. 100% right; 100% of the time. If you hesitated; if you panicked; if you hit it "pretty close" instead of 100%, you got to die. No deposit; no return.
When you look at an active shooter scenario, it's basically worst case...a crazy killer on a suicide run, lots of bystanders, panic, a staggering overload of often conflicting information confronting the good person. And at the bottom of everything is the simple question: "Can you 100% deliver the shot?" I don't know of any way to answer that question except through training and experience.
Every time I've advised a person or persons who wanted to get a firearm for protection, I've pushed hard on three points 1) how much are you willing to shoot. 2) how much are you willing to train and 3) what are your personal limits when it comes to defending yourself. I'm not saying that a person can't do an outstanding job of defending their home with a shotgun and minimal training; but that doesn't prepare that person for a worst case situation any more than a high school drivers ed class prepares your for a few 200 mph laps at Daytona.
And, heck, I haven't even touched on "stress innoculation!" I remember a SWAT training exercise we cooked up in mid-1980s. Officers had to run a pretty aggressive obstacle course before running onto the range. The first shot was 35 yards and the officer had to take cover behind a 3-foot wall. One of my jobs was as soon as the tired, winded officer drew a bead on the target — usually using the wall as support — was to tip the wall over onto the officer. Once they picked out the splinters, they never again "hugged" cover or used it as a rest.
I realize this is equivocal, but I hope it helps!
Michael B