Potty training is really hard for both people concerned: on the one had there is a parent striving to do 'the right thing' and understandably feeling full of self-doubt about where they could possibly be going wrong I it doesn't succeed, and on the other hand a little person who is not ready, for whatever reason, possibly a reason that will never be known, but who also feels inadequate, not realising how easily achievable the whole thing can be (nor can be reasonably expected to see it trough the eyes of an adult).
So it can feel like a desperate state of stalemate. Why is it these challenges make us believe they will never be overcome?!!!
It's a real shame that, as a society we have accepted 'norms' and timelines for kids who mature at different rates. Potty training is one of many such milestones. Others may not rear they ugly heads until school when someone isn't learning to read 'on time' or maybe doesn't get into the right college. Or perhaps can't have children of their own. Failure failure failure. Or so people feel.
Years ago, parents were taught to potty train ridiculously early, long before a child was ready. Nowadays there are jokes about how it was the parents being trained to spot the wee-wriggle and try to get there in time!
Having said that, it is really hard for people who are doing their best, to find their work isn't paying off.
Out of interest, what does your health visitor make of it all?
One thing is for sure, no one (without medical problems obviously) is still in nappies as a 16 year old. So they all get it eventually.
One other thing that crossed my mind - I'm sure you've heard of the fight and flight mechanism? Part of the physiological response sometimes involves withholding urine and faeces, because the body shuts down through tension. For that reason it's a really good idea to try to keep everything as low-key and relaxed as possible. It can't do any harm and will only serve to help both parties involved 