Hello,
I want to learn faster a piece, but if I get it quickly, I am not going to play the piece as it should be (eg. timing problems, rhythm, don't play the right notes, wrong finger position, etc). A teacher told me that it can be "corroded", it can be spoiled if I don't learned it correctly.

I know that I have to be more patient and go to the next part of the piece once I have understood the part I am learning, but it can also lead me to staleness if I don't know when I am ready to continue. (or if my fuel of motivation becomes empty

)
How can I know that I can advance to the next part of the piece?, what professional pianists do in order to learn a piece (specially a big one like a Mozart's, Schubert's Sonata or a Chopin's Ballade) faster without spoiling the piece?