Since I'm a juggler, and I've taught juggling, and been to many juggling conventions teaching Alexander Technique to jugglers who were much better jugglers than I will ever be, I wanted to say a few things about what I observed in people who can juggle and who try to be better jugglers.
Juggling and musicianship are obvious proofs that someone may be successful at an unbelievable high level of skill in spite of their personal self-imposed limitations. I believe that following a means of practicing that results in continuing improvement is an example of "good use," merely because it is effective.
First off, most people who do not juggle have no idea how much jugglers practice to perform successfully, just as people do not realize how much it is necessary for musicians to practice.
Practicing itself will teach quite a bit of what constitutes "constructive control". The way that a person practices will determine if they continue to get better or if they "plateau" or practice toward diminishing returns. Most jugglers quickly lose their progress if they stop practicing some of what they used to be able to do. Whereas those with natural "good use" seem to keep the memory of having learned whatever they used to be able to do much easier and longer.
Most jugglers leave out 'conscious' (The Alexander Technique definition of creative constructive conscious control) from their practice, and merely instill their routines into their 'body learning'; mostly because jugglers assume that they can learn faster by rote - or that learning by rote is the only way to excellence. Jugglers who overcome their bad use do it through sheer willpower of more and more practice, in spite of which ever "bad" posture they must overcome.
Check out this video of a juggler who we think has succeeded in spite of his limitations:
now compare him to this other juggler, Greg Kennedy: Greg, juggling easier
Essentially, most jugglers do not know exactly how they can juggle - which is proven in the classic ways they teach beginners to juggle. This common method excludes those people who are not talented with some degree of natural good use and the luck of having had accurate example and instruction from their parents on how to easily toss a ball.
I've explained some of these mystery factors of juggling for those who were not so lucky from my experiences teaching over three thousand people to juggle. You can see an example of the unusual way I have taught people in these pages:short version
For those who really want to learn to juggle, the thorough version: thorough version
If you read the instructions in the first link, you'll see how Chris Bliss has retained some of the assumptions it addresses and succeeded in spite of them. However, Chris Bliss may be "hamming it up" by imitating the common problems of beginners, such as staring & keeping ones eyes on the ball - we don't really know. We do know that the most dangerous theatrical high wire act in the business is the one where the clown up high repeatedly 'fakes' falling off the wire and saves himself at the last moment again and again.
Many jugglers rarely learn anything new, because they will just repeat what they know well to make it better and keep it up to snuff. As an accomplished juggler learns to do something, they then immediately learn to break the habit they previously trained. That's what makes them a better juggler, that they continue to learn. Usually there is no instruction in "how" to actually do these things - only dropping and dropping until they find some way to do it without dropping.
A few strategies do exist among jugglers; one is to attempt things that you believe are not possible for you, then to return to what you do know - the effect is, it makes what you do know completely reliable and easy. Of course, there are many of these learning tricks among certain jugglers that come forward in juggling conventions, but there is no codified pedagogy. I would speculate that those who have what is known by Alexander Technique as having "good use" have no idea how or why they are successful. Because of this, they are lousy teachers to people who have the problems that Alexander Technique can help with.
A juggler who has had some success but has not yet completely learned a new trick calls it, "being able to flash." This means they can sort of do the new trick but they cannot sustain it reliably. I could put my AT trained hands on someone in this situation and suddenly, they would sustain the new pattern... Some were even able to retain this sudden insight. Particularly it was interesting when I was assigned to "launch" people who were learning to ride a unicycle who already knew how to juggle and were trying to do the two actions together.
These jugglers did not know what to make of how that would happen when I would help them -other people who launched them did not have the same effect. Somehow, the people I knew assigned it's operation to making sexual attraction jokes because touch seemed to be required. ;o)
Goes to show you what people will imagine when they don't know why something works the way it does.