There is a tendency, especially in the modern martial arts, for one to aspire to be the top performer in their preferred practice, be it karate, jūdō, wrestling, MMA, etc. This however tends to drive one towards sheer training, pure unbridled physical drilling. It is however, quite obvious, to me at least, that the fabled masters of a bygone era didn’t acquire their mystical level of performance by pure practice.
In the classical martial arts (as opposed to tradition; archived into traditional ritual), there was not the concept of black belts, ascension to “grand masters”, etc., instead the layout of the pedagogy in koryū (classical currents) often begins at an initial transmission (shoden), then delves into a middle transmission (chuden), and finally the deepest transmission (okuden).
One aspect of this is that just like the contemporary practice of combative sports today, one could proceed in their whole career in the gym and in the ring (or octagon for the more pedantic out there). The classical master certainly could have done this as well, but why, instead, did they chose to instead head into isolation in the mountains, forests, and ravines? These masters were driven to something different, something deeper, almost religious in their practice. In every case, this was how the quintessence (Gokui) of their school (ryūha) was developed, polished, and to a certain extant, codified.
One of the reasons that just sheer training in repetition and conditioning the body and techniques in a gym doesn’t usually bring about the birth of such insights as these gokui is that the gokui is not simply about the most effective technique, or best strategy against different fighters. Instead, much of it is a matter of how one organizes and computes dynamic information in action.
Drilling, sparring, and dueling in a ring, gym, or dōjō can be good for best case scenarios, but training in the dōjō will never make you an effective fighter in a forest. Whereas the gokui needs to be applicable anywhere, at any time, against any opponent.
Context aside, the gokui is located deep in a practice, in the mind and heart (kokoro) of the practitioner. It is very much a mater of neuro-plasticity; the mind is shaped by profound experiences. When one’s practice becomes profound, their techniques, strategies, and understanding of a situation becomes a mater of feeling, which is far faster and more efficient for impromptu critical decision making than human cognitive processing. This is a reason why many modern martial arts speak out against “technique dependent” arts and praise “dynamic” or “principle based” martial arts.
The paradox is to go deeper in a practice in order to ascend higher.