In a previous post, I discussed the point of contact in terms of vector components. When you penetrate your opponent’s sphere, you pass the diameter line of the virtual sphere at the point of contact and have technically passed your opponent’s defense. However, just getting past the diameter line is necessary but not sufficient.
One mistake that I frequently made (and probably still frequently make) is to roll and pivot past the diameter line and attack straight away. That tends to only work if you partner or opponent is not attentive to your actions. The problem arises from the fact the force interactions are multidimensional. The point of contact is not a static sphere; rather, it is a dynamic point that changes curvature and moves in space.
Just touching the other side of the diameter line only means you have entered the sphere of defense. It does not necessarily mean you have an appropriate application point. You can penetrate the sphere but still give your opponent enough space to recover as you attack. In essence, your opponent readjusts his sphere to intercept your attack and re-establish your contact outside of the sphere.
To reach a usable point of application, it may be necessary to pierce in–or penetrate further into the sphere–to get the proper spacing for offense.
I realize my above illustrations are somewhat on the abstract side. I blame my engineering training for my love of abstract, idealized models. The concept can be felt readily, or observed as Sifu Sam Chin explains it: