Most modern hand-to-hand combat systems have gained a part of their superior efficiency by discarding traditional principles and techniques that have originally been developed to deal with opponents wearing medieval body armors. Instead, they are using more efficient straightforward aggressive techniques.

But if your opponent is wearing e.g. a protective groin cup, your groin kick will fail; if he is wearing protective knee cups, your oblique kick will fail; if he is wearing a bulletproof vest, your lat or nipple bite will fail; if he is wearing shin guards, your destructions against his legs will fail; if he is wearing a full face motorcycle helmet, your eye jab, ear slap, elbow strike, and even your headbutt will fail; if he is wearing protective gloves in a stick fight, your disarming smash will fail, and so on... You can effectively protect almost every part of the body against strike impacts, and many types of modern combat suits used by military and law enforcement units make even use of high-tech materials, not to mention the ongoing development of powered exoskeletons... (And someday, there will be cheap joint protectors preventing your opponent's joints from being hyperextended, which will even make your joint locks - as used in traditional systems - fail.)

This is what now re-increases the demand for the old "anti-armor" techniques of many traditional martial arts focusing on throws, joint locks, and the like. But the problem is that these techniques are typically the weaker choice against an unarmored opponent, and, also typically, require much more time and effort to be learnt.

Against each particular kind of attack, you can have one reliable conditioned reflex response available. An in-parallel conditioning which additionally differentiates between unarmored and armored opponents would be too complex and therefore lead to a disaster when being under stress.

So, what kind of technique should be trained against a certain strike?

As soon as you get aware of the realistic options, you find yourself caught in the dilemma of having to opt either for a highly effective system against unarmored men, hoping to never come across any body-armored opponent - or for an armor-handling system, hoping to never come across any skilled unarmored opponent... - Or you should consider wearing full body armor every day...