What we seem to be examining here is a mindset. The "one hit kill" principle can be trained in different mindsets. I know that I personally train to attempt to knock out with most strikes, though I train with the understanding that I will likely be required to use more than one or two strikes to end a fight. In fact, most of my no mind techniques usually utilize 8, 10, 12, or even 15 or 16 strikes before I move to finish. I also train with the mentality that I never know who has my opponent's back or what they have in their pocket, and so I do not train to strike and run; I train to put my opponent to the floor and finish him/her. A "finish" in my mindset of training means that my attacker can physically no longer fight or chase after me. If this means that they threw one punch and I threw 8, took them to the floor, and broke their knee, that's ok with me, because I now know that they can't fight with me anymore. If I have a legitimate reason to believe my attacker has a gun, then I will not stop until I have it in my controlled possession or they are knocked out. Back to the "one hit kill." I do believe, though I've never witnessed, that there exists the possibility to kill an opponent with one hit. I know from experience that one hit can end a fight and knock someone out if it's in the right spot or the striker is a bit lucky. As I said though, I don't train with the expectation that this will happen, and I think it is very dangerous to train with any kind of expectations like that. I do, however, train with the mentality that I should be using my power strikes to attempt to end the fight, and of course my mentality is to never start a fight, but to always finish a fight.