Theory, perspective, balance, and martial application.
I believe that here lies the key and the root to all of our martial applications. Yin/Yang is the perfect theory, flawless from all angles due to its self justification. Everything is relevant from a certain perspective.
To illustrate, I will use one of Grand Master Rick Moneymaker's analogies. Compared to an orange, the color of a lime is dark. But on the other hand, when you compare that same lime to a plum, the lime is lighter in color. Thus, there is no absolute when dealing with Yin and Yang, except that it is always dynamic.
What is Yin can be Yang and Yang can become Yin. Confused yet?
It is always dynamic.
Let's take the quadrant theory for instance. Imagine the quadrants while facing the opponent. You know that by hitting quadrant number 1, the greatest effect will come from the following strike to quadrant 8.
However, if you were already behind the opponent, then hitting quadrant number 5 and then going to quadrant number 4 would have the greatest effect. Too often we lock something in our brain, like quadrant 1 to 8 has the greatest effect. But this is relevant to your relationship with the opponent.
This will make sense assuming you understand the quadrant theory.
More to come but I'm tired.