Perhaps ‘secret’ is to charged a word for the way many systems were passed.
Should we consider a better term, like ‘reserved’? That signifies those training practices might have been taught only when in the instructor’s experiences the student was appropriately prepared for those studies.
Those systems which I have trained that ‘reserve’ their training for appropriate student development do have a ‘secret’, one that moves across the board. That there is a synergy that requires the development of the whole system of training to express those teachings. Appropriate force enhancement isn’t a question of one application, one new form or weapons study or perhaps a new principle.
As a general example there is the issue of ‘spirit’ and the student. The instructor’s decades of development from actually believing the form makes many applications inappropriate for the student who hasn’t reached that level of execution. Those applications are ‘reserved’ for those who have those years. To share them when the student does not have decades of makiwara behind them, and true belief in the technique to perform it without changes less important. So those movement applications are not shared until the student develops. The student then is a participant in the knowledge release. If that knowledge becomes lost because of students inactions (Advertent or inadvertent) that is the natural progression of time, imo. Sharing to any who don’t fully possess those skills is in itself surety that it won’t propagate them.
Other arts are family traditions. Why should others outside of that tradition possess that training? If you aren’t there, does your need require them to bend to your wish? In many senses you don’t even know what that tradition requires. Back to the synergy issue. The skills are often all requited.
Let me provide an example. One of my friends spent over spending 25 years learning Faan Tzi Ying Jow Pai. If you are familiar with Chinese systems many of them possess components of training such as Chin Na (grappling techniques). Though seemingly similar to potential karate applications, it is often very different. Ying Jow Pai specializes in Clawing technique with the full hand. But the key is the claw they use becomes a force enhancer to the locks employed. Effective as with decades of work the claw is most akin to use of the hand like pliers. The pain from the grip enhances the movements. The use of the grip is seen in claw like marks remaining behind for weeks where applied. But the key is, first 10 beginning studies of the Chin Wo, decades of form study, supplemental drills, multitudes of weapons systems, two person forms and unique sparring practices all combine together to make the claws fists so effective. Even the two person forms contribute multiple layers, both how to use the claws offensively and the countering of those techniques.
Trying to understand a tradition and picking and choosing it should be saved still means the loss of the larger synergy.
So ‘secrets’ can often be misunderstood. That is why I suggest a change is appropriate.