Up until very recently my policy used to be "learn a piece, master it, move on to a new one". This sounds quite logical and I belive it's what lots of amateurs/beginners do. This method is also frecuently used as an excuse not to learn new pieces, because it's a well known fact that starting from cero a certain piece means much more work than simply playing the ones you already know.
My family was getting more and more fed up with my practicing, and I totally understand them, because it's really annoying to have to listen to the same pieces day and night, and every time the same mistake in the same passage. I had got into a vicious circle of no improvement whatsoever, so finally I said "to hell with it" and took on two pieces I had had on my "waiting list" for a long time.
Here's my surprise: I found that these new pieces contained challenges that where similar to many I used to have trouble with in the old pieces. My first reaction was "well, I guess this is as far as I can get", but what do you know? I realized that having a similar problem in a different piece may actually help you fix it (you could say, it's like it helps you "see" the problem from a different perspective, in a different context). Not only was I able to figure out how to play those passages in the new pieces, but I could also correct my playing of the old ones.
So, my conclusion to all of this is: when you're stuck with a certain problem on a certain piece, it may be okay to practice it a few times more, but if you just can't work it out, moving on does not mean skipping the obstacle, but rather a good way of getting a whole new view of it that might help you solve it much better that sticking with that first piece.
What do you think about this? Am I talking nonesense?