This thread has been interesting... The biggest argument seems to be "what is the correct data set to use" when determining whether wrist locks work.
But, what am I to take from reading 7 pages of this? In my art, we do study wrist locks. Should I accept one data set and dismiss them? Or should I take the other data set and just practice harder? Or should I redefine "works?" Here is my take away from this thread.
You need to define for yourself, what you mean when you say "I have learned this wrist lock and can use it." Does this mean that you watched it on youtube? Does this mean you were shown for a few minutes? Does this mean you have applied it successfully against willing partners? Have you applied it against semi compliant partners? Have you applied it against full resistance? Have you applied it against full resistance against people not from your school, possibly with a different rule set? Have you used it in competition? Have you used it in a real situation on the street?
In reality, you will have different answers for each technique. If you have only ever applied them in the school, in prearranged set ups... its important to know that, before relying on that technique for something more important.
There are some wrist locks that when I say "I have learned this wrist lock," I mean I have used it in my school, in the prearranged drills, I have used it in sparring inside my school, outside my school, outside my style and with people of many different styles, under different rule sets, with full resistance. And when I say "used" I mean they "worked" by either getting the person to tap or go to the ground. There is a greater number of wrist locks, that when I say "I have learned this wrist lock," it means I can do the demos, and apply the lock in the prearranged drill, that my school uses, and that is all. It is important that I know which is which.
I take time to train with other people, in other styles, with other rules and different ways of doing randori. Once I have built a good training relationship with other folks, I will try to put in my wrist locks to see what happens. (its important to develop a good relationship, so that the people you train with understand that you are testing yourself and your training, not trying to take cheap shots or make anyone look bad... except maybe yourself) I have had way more wrist locks fail, than succeed. But, instead of getting frustrated, I go back to the drawing board, and try to figure out what I am doing wrong. For some locks, I have figured out pretty decent ways to set them up and apply them. Others, I am still working on. Still others.... well lets say I still get countered a lot.
Here is the real kicker though. You can read what I said about trying out wrist locks and conclude that wrist locks suck and I shouldn't waste time trying to learn them. But the point still stands. You should be able to take out every instance where I said "wrist lock" and put in "straight right," "double leg take down," "rear naked choke" and "round house kick to the head." Whatever it is that you train, you need to try multiple forms of resistance, against multiple people, from different schools, different rules. So that when you say "I have learned to do X," you understand when and where you were able to be successful with that technique and how much more you need to test that technique. Your "go to bag of techniques" should be the one's you know that you have tested the most.
Every technique is going to start with the "I saw it on youtube" or "I was shown it in class once." They all then move through the various drill, repetition, scenario set up and randori type situations in your school. Then it is on the student to get out of the house and try those in different places, with different people, with more and more resistance. (yes, you may need to go outside your school to do this. Your instructor may not help you with this... but its your training, not his.) If you don't get out and pressure test what you learn... that is also valuable information for you to know and for those who you may teach this stuff to, to know.