I'm learning melodeon. A few weeks ago I had reached a point where I was ready to give up as I felt I was making no progress. Then, one week our regular tutor was away and we had a different one that week and he did something which unlocked the problem I was having (co-ordinating left and right hand doing different things) and once again I was making progress. It was not that the regular tutor was poor - far from it he is excellent and very supportive - it was just that a different approach helped overcome the immediate problem. We all go through these plateaus when learning something new and different things can help us start to progress again. Coming at a problem from a different angle usually helps. I also agree with those who say put it down for a while and come back to it (but don't leave it too long). I have often found this helps when I am learning a difficult piece.