AFAIK personal attitude is the main driver for failures. Not being Japanese "compatible" so i heard, whatever it means. That's how some of the guys put it for me. Also each and every company has to show the authority a failure rate as it wouldn't be normal according to their books that everyone or most of trainees pass. Some companies don't have their own checkers so the authority is doing the job for them. It must have something to do with the culture I guess.