Imi was a unique example for how a Krav Maga technique is changed. He himself did not teach a system, he taught techniques, and my job was to build it all; the curriculum, techniques, training methods, principles and tactics as an integrated technical and tactical system.
Many times I saw how Imi change his mind and his techniques. Sometimes it was due to a change in the way the attacker act; sometimes he understood better the natural response of the defender or the reaction of the attacker; sometimes it was his logic that brought insight and understanding why this or that element should be changed.
However, sometimes the need and insight came from impact, as the technique did not solve the problem and failed.
One example I clearly recall as it cause Imi to bleed. Blood was the catalyst for a change.
It was during our first trip to the USA, when we were demonstrating KM to the local Jewish communities.
During one of the demonstrations, Imi, then 71 years old, did a defense against a straight stab with a knife. Back then, the technique to the live side was done with a small body defense, inside forearm defense and a counter attack of straight punch with the fist that is upside down. The attack was done with a real knife with a relatively heavy blade. The defense was with the right hand against a right handed knife attacker, and hit the wrist of the attacker. The knife attack was bit inward, as it is naturally done, the attacker’s wrist was bent a bit and the knife hit Imi’s throat and cut him just a bit, like a shaving cut.
That moment Imi understood that the technique was wrong and needed a change. He concluded that longer time- and distance-defense is needed. He started doing a sweeping defense that redirects and leads the attack away from the target, using a larger body defense and torque.
Later this principle was better understood and now is used in several solutions against different attacks as sidekick; left punch defense with the left palm; some releases against close range choke and headlock from behind (blood/artery restraint), and more.