Gamer friends of plurk: what is the best advice for one slowly, slowly learning to play with a controller (and being really good at believing X is a, and b doesn't exist at all)? 
Y is great, though. Y and I have an understanding.
I'd probably start with games like fighting games (mortal kombat sort of thing). It's a fast way of learning buttons because certain combinations use different buttons
Be persistent!! Games aimed at kids can be helpful—they’re usually more forgiving and hold your hand more.
Personally I don't even mentally acknowledge which button is which. I just get it into my muscle memory where my finger needs to be to make a thing happen.
Since most games these days use semi-regularized schemes it works just as well as actually learning the buttons. Like usually the bottom face button is some kind of attack or jump, the top face button is usually a menu or item, left trigger is aim, right trigger is shoot, etc.
Even if you swap between systems almost everything has that same basic setup these days; even the Switch does