.....what do you do to hold onto it?
Some days everything seems to go right: tone and intonation are great, low register is steady and sonorous, upper register clear and silvery, you start centring every attack, and a few articulations that had been giving trouble just fall neatly into place...
For an hour or so maybe.
But then what do you do? Do you quit when you're at the top of the game, or just keep practising until you drop, trying to get as much of that magic embedded as possible, fearing that next morning "the knack" will have vanished never to return?