MSGT Benavidez has got to be one of the hardest men that ever walked the earth. I've got a biography about him that includes photocopies of his medical records.... they're unreal. The fact that he died of old age is a testament to the sheer force of will that man possessed.
I was going to post something along these lines in the purse fight about needing to kill people to know how to kill people (or whatever the hell everyone was arguing about in that thread about a cop winning a gunfight); We can kill people a couple of different ways. Punch holes in the plumbing or shut down the electrical.
Shutting down the electrical system is by far the most efficient method. It's also a pain in the ass to get right. Turns out the head moves.. a lot. Particularly at close range when the guy whose electrical system you're trying to switch off doesn't want to be cooperative.
The other option is to punch holes in the plumbing. We get the fluid coming out and the air going in and the system stops working. Unfortunately (especially if we're working under a time crunch) this doesn't necessarily happen fast. A man can be dead as a door nail but not know it. He can also make life miserable for you and anyone else until his body get's the message. Rule of thumb - If it's man-portable it shouldn't be relied on to stop the fight RFN. That's why we train failure to stop drills and non-standard response. You might have killed the dude, he just hasn't gotten the memo yet.
At the end of the day, the other guy gets a vote in any violent encounter. People under the influence of mind altering substances, true believers or simple hard cases might all die a little or a lot harder than the average bear.
Case in point; Sgt. Michael Hodshire was killed by an IED in Iraq in Oct of '05. When the device detonated he was struck in the head by shrapnel that went under his helmet, blew a hole in his skull and exposed grey matter. Mike got out of the truck, emptied his magazine in the direction of contact and dropped. Now he was dead as soon as that chunk of metal hit him, but either his body didn't know it or he just didn't freakin' care. Some dudes die hard.
Training, mindset, fitness, and conviction can all play a role. Don't train to fight some gangbanger with a Jennings. Train to fight your nightmare foe on their best day. Worst case scenario, go down swinging. That's really all any of us can ask.