Contradictory to the principles of Yin & Yang, many styles of martial arts such as Karate, attempt to block the on coming blow.  A block is a Yang action, whereas a parry is Yin.  The block uses force to stop or deaden the blow while the parry softly redirects it.  Utilizing a block pits Yang against Yang.  Its success depends on having the strength to overcome the attack.  Meanwhile, the parry balances the situation by using Yin to avoid the Yang.  COUNTER ATTACK! The launching of a counter attack also depends on  Yin &  Yang.  While the opponent attacks with the jab (Yang), you evade (Yin), slipping underneath the blow, you strike to the ribs (becoming Yang).  His reaction is Yin as he recoils in pain. This is a perfect example of  "fitting in" or adapting to the situation.  You have made his attack your attack! While still following Yin & Yang, there are an infinite amount of counters that would work in this situation.  Experiment with it! INITIATION OF ATTACK It is not necessary to wait until you are attacked to utilize this strategy.  There are many ways to initiate the engagement with Yin & Yang in mind. For example, if an adversary stands idle, unsure of his attack, moving forward you can press him (Yang) forcing him to react.  If he reacts by stepping to the left (Yin), you can intercept his motion with a hook punch, using his movement against him.  If he reacts with an attack to keep you away, you simply "fit in", striking him at a moment where he is vulnerable.  Another method would be to leave yourself open as a decoy.  Hoping the opponent attempts to take advantage of that opening, you are ready with the appropriate response.  Being open you are Yin, attacking your weakness he is Yang.  Or the opposite may be true.  Being mischievous and controlling his actions you are Yang.  His falling for your ploy makes him Yin.  Regardless of how it is perceived  the out come is the same.  The action ends with you striking him (Yang) and he, once again, recoils in pain (Yin).        THE VERSATILITY Yin & Yang are the perfect strategy for any adversary.  No matter the situation there is always a Yin and always a Yang.  It's not like having a strategy that fails when the situation presented is not ideal for that action. A specific game plan never works.  An art that is built on one strategy alone is Tai Kwon Do.  Their main goal is to kick their opponent in the head.  The idea behind this is that the legs are the strongest weapons and the head is a most vulnerable target.  The failing in this plan is two fold.  First, the head as a target is relatively hard to hit with the feet as compared to others such as the knee or the groin.  The second is that it doesn't take in consideration the fact that they may run into a puncher that gets inside those kicks.  Having concentrated on their primary goal, they are caught unprepared for fighting in this range.  Their kicks are superior but by neglecting their hands they are defeated.      A well thought out strategy leaves room for variables.  One does not attempt to plan out the engagement step by step. He cannot create a counter for every attack.  He cannot completely dictate the actions of his adversary.  A fight is "alive", it is ever changing and the variables are endless.  Yin and Yang; what better strategy to adopt?  It too is alive, ever changing, varies to infinity.  Discover the Yin and the Yang and you will see things as they are and not how they should be.