Re: significance to testing/belt rank?
"Even if the chance of failing a test in the organizations I mentioned is as high as 20%, and I doubt that it is that high, perhaps the pressure could still be increased by making the failure rate higher"
Just sort of playing devil's advocate here, but wouldn't that depend also on the 'consequences' of failing, even (or perhaps especially) the psychological consequences? I wonder if failure was _very very_ common, if there might actually be less fear of failure because 'it's no big deal, it happens to everyone all the time'? I don't know if that would actually be the case (or maybe if might just shift it from 'fear of failure' to 'really hoping you can pass' and make passing that much more exciting and rewarding, which could be a motivator too), but I do think if failure is a minority but possible if it makes you really not want to be 'that one that everyone will remember who failed' or however you may picture it in your mind.
In any case to me personally it's more important mainly to 'know that I really honestly passed', so I would just be suspicious if testing and grading seemed too automatic or arbitrary.