We would all like to be prepared for that encounter, we have "My gunfight" inscribed on our brain it is what we prepare for. We have all heard 3 shots in 3 seconds from 3 feet, well I have bad news. While those statistics are real, they are from gunfights that cops died in. First of all how do we get "Average" well, we throw them all in a pot, boil em down and see what we get. The first thing to understand is that if you get into a gunfight it is already a mathematical anomaly, so now we are going to prepare for "average".
Do you want to survive the fight? Of course you do. You must dominate the fight. In order to dominate, you must first recognize that "Hey, this guy is attacking me!". You must seize and maintain the initiative with surprise and violence of action, which comes from military doctrine of, surprise, initiative and violence of action.. There are some very bad people out there, some freak just killed and dismembered a little girl in Denver. Are you prepared to meet that kind of evil face to face?
Of course this is my opinion so take it for what it is worth. Carry enough gun. The only reliable way to stop a violent attack is to hit the CNS with a decisive blow, that means upper third of the spine or the brain. Head shots are iffy at best, to hit the spine you must first punch through the BG. The wiz bang HP that dumps its energy and does not penetrate probably will not do the trick. Provided that you just delivered several "well placed" shots be prepared, the BG may not stop for several seconds. There was a BG shot thru the heart with a 230 Grn 45 ACP GD who ran 3 blocks before expiring not long ago. There is no such thing as a magic bullet.
Master your carry gun. Can you run it without conscious thought? Can you hit that 3"X5" target at 10 yards ? 15? Yes it takes practice, it takes commitment. I recently realized that buying the gun was the inexpensive part of the equation.