History of the term Il kyok pilsal (일격필살) (Ikken hissatsu)Many authors seems to agree that this term while being present in the root arts of Taekwondo (Karate) dating back to the 1800s was originally used in weapons based martial arts. There are also many sources claiming that this term came into Karate usage after it was exported from Okinawa to Japan in the 1920s onward as an influence from Kendo. Kendo being a martial art based on the usage of swords it seems to be a reasonable explanation for where the term came from but personally I believe it was part of the Karate mentality even before they exported it to Japan. It could very well be that the term did come from Japanese weapons based martial art however since it is known that several Karate masters had extensive training in Jigen Ryu which was the Satsuma Samurai clans martial art. Bushi Matsumura and Azato Anko both teachers of Gichin Funakoshi both had mastered this art at a high level and in "Karate Do My way of life" Gichin Funakoshi tells us that Azato taught him Karate With a mindset that the opponents hands should be thought as if being swords. No matter where the term did came from we do know it was pretty "popular" and well known after Karate was exported to Japan and we do know that Taekwondo`s original Kwan founders practised and studied Karate during this era which also explains why the translated term came into usage in the different Taekwondo Kwan (schools).
Meaning of the termI have allready translated it as "One strike, one kill" and it seems very straight forward but I think that it is often missunderstood the term. Like "There is no first strike in Karate/Taekwondo" many people interpret the term as is without any thought or critical thinking present. We know that both Karate and Taekwondo techniques can be fatal if used in a lethal way. You do not have to look hard to see that, as knife hand strikes to the neck, neck cranks, and stomping someone who is on the ground could all easily be used as lethal strikes and all these are present in many Taekwondo Poomsae, but at the same time we know that many strikes, locks and throws can cetainly be lethal but usually they are not. You can kick someone in the ankle and they can fall down and hit their head and die so there is no such thing as a "safe" place to attack your enemy and this is the first meaning of the term in my opinion. As a moral and ethical reminder that everything we do can result in a death even in one move, one strike or even push. It is quite sobering and removes many preconceptions when you Google stuff like one punch kills etc and see all the news stories out there where people have indeed been killed by one punch. Often it is the fall that kills them not the punch itself but it happens quite more often than what you believe.
The other meaning is one that I believe is the martial goal and describe the mind set we have in Taekwondo when we train and when we look to our Poomsae for combative meaning. Some think that one strike one kill is the ultimate goal of Taekwondo so they practise single punches and believe that their single punch should be able to end all physical conflicts. I believe it is much more a term describing the mindset rather than the actual result. I take the term to mean that we should strive to end the conflict with one move, in other words as quickly as possible. The goal is not to kill the enemy but to deter him from pressing on his attack. Wether that is by shock, knockout or whatever is besides the point. It also tells us that sportive tactics like feinting an attack or going into a half hearted attack is not the way of Taekwondo. In a real conflict you will most probably be facing an untrained opponent. He can be very dangerous and depending on the setting he can be much more accustomed to real violence than yourself even if he has no formal training. Feinting an attack works by taking advantage of trained responses in a competition format. I have no doubt in my mind that they are effective, but feinting in a real attack will only take away precous time and energy. You will likely not be able to provoce any trained responses anyway, even if the enemy is trained simply because of the effects of adrenalin.
Going into a half hearted attack is often done in sports too, but you do not afford this in real life. In a real encounter you need to take as few risks as possible, and when you do go on the offensive you need to do it with all your mind body and heart. You might just get that one chance so make the most of it.