That is probably one of the most common phrases about practising - Practise until it's perfect.
I don't really know about that... Many times, I feel like the more I pracise, the worse I play. Ofc it's a bit too simple to say it like that. Like an example:
I play the 2nd ballade by Chopin. First I practised a lot on it. Then I let it rest for a while, and now I've brought it up again. The first playt trhough was, ofc, not very good. But the second was actually very much better, and the third (after just a bit of practising) was even better again. Then it went not as well after that. It wasn't bad, but it wasn't as good as it was before.
(not note wise, or really musically. But the excitement of playing somewhat disapears)
And then there is the other thing: Practising a halv new piece, and try to make it perfect. I mean, everyone knows that you can't play every note perfectly. Sometimes not even a phrase. If one tried to practise until it was perfect, we wouldn't really get that much done, would we?
So, when do you stop practising?
Is it when you've got the main idea, or a bit later than that, or maybe even before you get the main idea? And how do you feel it's working out for you?