I don't recall every reading a thread on this topic. It's been my experience that impediments to one progress are mostly learned impediments, caused by invalid memory, both short term and long term. This thread concerns identifying why one stalls out in their progress. So, without further ado, technical plateaus can be caused by the following...
1. Faulty Mechanics. This is often the primary problem. An example of proper mechanics would be curved left-hand fingers, or a rest-stroke from the open-hand position. It's been my experience that plateaued students are not able to diagnose their mechanical problems, and are even more unfamiliar with appropriate remedial drill/etudes. This evaluation/remedy model is one of the roles of the teacher. Even one lesson or a master -class can make a world of difference with identifying and remediating some of your faulty mechanics. As you have discovered, these can be ghastly to correct since they reside in motor memory. Practice makes permanent, remember?
2. Inappropriately combined mechanics, also known as techniques. This is another motor-memory plateau (your brain performs complex combinations of mechanics, without conscious control). I call this level of study Segment Practice, or the stage at which the student investigates, discovers, and drives into motor memory the most economical solution to technical issues. These solutions are often different for different players. A segment has 5-9 individual mechanics, since this is the range of short-term memory. As an example, think of a segment in a Sor study as 1 measure plus one beat of music. A teacher can help the student identify segments that will not be stage secure, and suggest appropriate modifications. Be prepared to spend several months (or years) with a teacher at this level of study. Many of my students study on and off for several months at a time, and then take a few months to consolidate their new skill.
3. Poorly rehearsed Phrase-level-segmentation. This is the combination of 5-9 segments into a phrase (including dynamics, articulations, etc.), that ends with a cadence. This is the musical-memory plateau (you can sing along with your playing), and is actually quite easy to navigate if you have selected your segments so that each contains material from the preceding and succeeding segments. In other words, your segment choices overlap. This is mostly done with back-chaining, for reasons of short term-memory transfer into long-term memory. Phrase-level segmentation can be done without a teacher if the students' mechanics and segment practice skills are secure. If insecure, the student is wasting pieces since it is hard to undo bad phrase-level segmentation. As a teacher, I try to combine this study with the following...
4. The realization that you’ve become a copyist. This is the plateau that can be the most frustrating, and rewarding. How do we make another person’s music meaningful? Can we give a unique performance? Why do we prefer artist X over artist Y? How can I as a performer stay interested in a piece? Tough questions, for sure. At this level the student is tasked with applying their skills with music theory, form and analysis, and musical style. They need to take ownership of the music and make it theirs. This can take a lifetime. A student once asked Pablo Casals why he practiced so hard at age 92, after retiring from the concert hall. His answer, "I think I'm improving". Do you really believe that at his skill level he was worried about mechanics? I suspect not. He was likely still trying to improve his already world-class interpretations.
If you know of other reasons for technical plateaus, please don't hesitate to contribute to this thread. There are many non-technical reasons for plateaus, such as indifference to technical matters, physical limitations, etc., but please limit the discussion to technical and learned reasons for stalling out in ones progress.
All the best,
P.S. This is a copy of a post I made in the technique sub-forum.
Dr. Lawrence A. McDonald, D.M.A., Art Kaplan Fellow
Author of The Conservatory Tutor for Guitar
2018 Michael Thames "Ancient Dragon" Cd/Ir
2008 Michael Thames Cd/Br
Royal Conservatory Advanced Guitar and Theory Instructor