When people become devoted to a martial art, they are doing so not at a single point in time but in a process that extends through time — the present moment, the memory they have of their training, and their expectations of the future.
Often very devoted practitioners cherish the first view they had of an art, when their inspiration and excitement was at its peak. Of course, when they began training they were also rote beginners at the practice, so not well qualified to judge the art, or even their experience learning it. As they learn arts that have layers to them (Shinkage-ryū being one good example, but the argument is more general), they may experience some distress, especially after thinking they have understood or become proficient with a portion of its teachings, when a teacher introduces another level to training, or provides information that seems to go against the grain of what they were first taught. Much of modern culture prizes linear processes, quick or slow, but advancement nonetheless. Instead, in traditional martial arts, we often experience plateaus of understanding that can persist for a long time (sometimes, indefinitely) that would need to be processed in some way to move through and beyond to greater levels of skill. Common is the mediocre swordsman.
A teacher has to judge when to show the student directly, when to prompt them indirectly, and when to simply watch and wait as the student struggles. Sometimes the student does not figure out how to swim — in the case of traditional swordsmanship one does not literally drown under such circumstances, but nevertheless the expereince can be stressful. Is the teacher simply not teaching? Do they not care about the student succeeding? Do they know something they will not share? Why are they indifferent to their student's suffering?
One perspective is that a practitioner should study under a teacher that shares their knowledge without reservation, but from the teacher's perspective they may indeed be doing so, only to have the student miss key details either by training with not enough attention (they think they 'know' the kata or principle) or intensity (they think they don't need to practice as much now they have reached a certain 'level' of training). Or their training is distracted by continued obligations they feel they have to other activities, but are irrelevant to their teacher (e.g., continuing to practice another martial arts). Or they are distracted within the group. They might think they should rework material for beginners they are mentoring, making it 'easier' for them to learn, or rework the curriculum of what they are learning to make it more 'common sense', thus destroying parts of its character they are in fact unaware of. The examples go on.
Of course, there are also teachers who cover up their limitations by pretending to know more than they do, and point to a myriad of reasons a student is not ready for more. Or they suffer other problems of character or behavior a student might only discover after many years. This narrative can cut both ways.
One specific example, in an art with layers to its practice, is when more sophisticated body mechanics are introduced to the practice.
A student who is a gifted athlete or naturally strong and agile might discount the refined body mechanics introduced in Asian martial arts if they have to that point excelled using their natural skill. They may be resistent to changes a teacher appears to be making, which are not changes to an art but instead revealing a more subtle manner in which the art can be practiced, once a person has some passing familiarity with it. The teacher is the same person the gifted student was excited to train with initially, but when the teacher introduces more sophisticated practices that challenge the very notion of natural strength and agility, the gifted student might be quite frustrated that their innate abilities (or cultivated, through western physical culture) are not good enough or being discounted. Especially if they view their teacher as not as strong or fast as agile as they are, due to age or some other factor.
These kind of internal narratives on the parts of students often assume the teacher's skill is fixed and not changing over time. In reality, teachers themselves continue to train and their understanding of arts mature and evolve. So, they are not the same people the student began training under. We train, we age, we teach, we take on new practices, sometimes let old practices go. It is not always the case that early students of a teacher are more fortunate, if the teacher's understanding has deepened over time. Each case will be unique. But as a teacher's understanding evolves, they very well can practice the same martial art with a new perspective, if they are aware of and preserve its guiding principles.
I mentioned the notion of nostalgia for early training. Maybe some practitioners feel the first way they trained was more authentic than later on, if a teacher has made some small modifications to how they practice an art. But if the teacher has a deeper understanding, those changes may be quite important to pay attention to, and not sometime to be quickly discounted. Once people get into a specific habit of thinking and movement, they feel good about a certain way of doing things. They want to build on that knowledge, and in a linear fashion it is appealing then to learn more kata, get ranks, feel like they approaching the end of an art...
Arts do not end with being awarded their final license.
The understanding of an art can have multiple layers of meaning. They way I do introductory Jiki Shinkage-ryū practice twenty years after beginning training should not be the same as I did when I first trained and was being watched by my teacher. If it was, the intervening time and effort served no purpose. But, ideally, the current practice would still be Jiki Shinkage-ryū, despite that changed understanding.
Arts that have a cohort of senior teachers that can interact and provide feedback to each other, collegially, tend to be stronger than ones that fracture and fracture as each generation passes. This is not a question of lineage. One can have a well-defined and accepted lineage and still not be very good, for example if an art was never very good to begin with, lost too much of its curriculum or higher-level knowledge or was taught to too many people, who thus did not learn the art at a deep enough level to convey it forward properly. This I believe was the case in the past with some lines of Jiki Shinkage-ryū and more recently with lines of Katori Shinto-ryū that have been taught to literally thousands of people.
This often accomplishes, in the end, nothing.
This article was inspired to listening to a senior US budoka suggesting an art needed a few hundred practitioners to survive. Knowing each school is quite small, that implied some kind of federation. Given the difficulty associated to transmitting these art forms, maybe having that size pool to sample from allows for there to be one or two people good enough to master the whole thing in a generation, but teaching a smaller group in a more dedicated fashion seems more appropriate to me.