There are martial arts that teach the single-hit-fight-ender strike, the so-call "one hit, one kill" theory. Back in my early karate days, there were guys with whom I spoke who absolutely believed it. One focused strike, they said -- usually a twisting punch fired from the hip -- and lights out, baby!
We, uh, don't subscribe to that theory in our art, for what we believe is a compelling reason:
It doesn't usually work. (Unless you are a sniper with a high-powered rifle, which is different.)
If you have a bored god smiling over your shoulder, then that patented smackdown shot might do the trick. If you are rolling sevens all night and hitting blackjack every draw, maybe that poke will end the job. You can blow the smoke off your knuckles, hum a little bit of the wah-wah from The Good, The Bad, and The Ugly, and go home, and more power to you.
If you carry a single-shot horse pistol in .60 caliber and you put that fat lead ball in the right place, it will take a man down sure enough, but --
-- but: people can be both fragile and extremely tough. Listen to stories by ER personnel, cops, jailers, bouncers who have seen guys with broken skulls and bones sticking through the skin who kept coming. People have been shot multiple times with high-powered handgun ammo and kept coming. You got a punch better than a magazine full of 9mm or .45 ACP?
I've seen guys knocked cold with a tap to the temple. I talked to a guy recently said he's seen guys take full-power shots to the temple and keep coming.
You will be safer to go with the assumption that the death-touch might not work -- and have an option if'n it doesn't.
Better a gun with more bullets than one, just, you know, you miss the first shot. Or it hits a Bible the miscreant carries in his coat pocket, or that pesky and miraculous Zippo lighter. Or a bone. Or even if it hits meat but he is too stupid to know he's dead ...
We like the HEA Concept ourselves: Hit 'em again.
Rinse, repeat, and continue until hostilities in your direction cease. No less, no more. If you apply this rule say, nine or ten times and the hostilities continue, then you might want to start looking for a brick or a tire iron or a blunderbuss with four or five hundred grains of black powder and a bunch of old nails and wheel weights ...