"Uncanny Valley" is a term I'm swiping from the computer generated visual effects industry. It's a term that describes the property of animated anthropomorphic/human depictions in that, as the animation technology goes from being "cartoony" to "perfectly realistic", it first looks stranger and stranger. You know you are looking at something fake but you're not sure why it's fake. But, you know the attempt to fool you visually is underway.
When people decide to pick up an instrument for the first time, what unfolds psychologically is something along the following graph:
|(ACME Depiction of Written Text)|
These sort of "landmarks" are places I have found myself having to almost play the role of psychologist, in attempting to mentally nudge someone to move beyond the mire of their present thought process. These places are traps. In fact, I could argue that these places are about the only thing that prevents anyone from advancing to whatever musical goal they aspire to.
More on that later, but for now - the Uncanny Valley:
The closer one gets to achieving Actual Mastery over a particular phrase, mechanical movement, or conceptual control, the more likely one will be satisfied before the optimum result.
The student practices, goes about their way in whatever fashion, and arrives at a "place" where they feel not only are they "getting it", but they're moving further ahead, into a "mastered" zone.
I've watched this happened right before me. For some people, they do the musical equivalent of passing out before the peak of the summit. They just stop trying any further. They're fine with having seen the top of Mount Nitaka.
Others will vacillate with pushing that last meter. Time to take a break. The nausea sets in.
Or tunnel vision happens, temporal distortion: that last meter suddenly seems infinitely far away, continued effort seems fruitless.
Now and then I get the the person that (in mountain biker parlance) bonks. They front loaded their effort too much. It seemed to gain them an advantage, at the expense of running out of steam. Lots of initial practice and vigor thrown at it, no reserve left over. Pacing.
That zone, the Uncanny Valley, can ensnare effectively anybody. Knowing it's going to happen, knowing that one is "there", perhaps can help one to see it through. The last 10% of effort is hard, but a lot easier if you know it's the last 10%. Stopping, giving up, tricking oneself over that 10% is a shame - you get all the way to that place, and that last 10% is where "professional" exists. You don't go on to something else, take a break, or come back to it later. It's the most tedious part of it, but also the most straightforward.