A lot of very sound advice here I feel. First started in brass bands in the UK and as I achieved positions in better bands it soon became evident it was an absolute necessity to be able to double and triple, indeed players who simply couldn't articulate the demanding test pieces for contests would simply be dismissed. All a little "hard" maybe but after enough chances to get it right one would simply not expect to remain if one didn't. Sounds a bit like the"school of hard knocks", but I was always fortunate to have experienced people on hand to help during my formative years. I think once learned never forgotten. Just gets a bit rusty when not used enough but as with all things music, keep on top of it and of course the best advice is lots and lots of lovely practice!