When I'm working through a piece such as the Second Movement of Clementi's Sonatina (op.36 no. 1) I find myself, more often than not, making the same mistakes over and over and it's driving me nuts! For example in the forth bar the triplet arps move down to the second inversion of the chord, and I can practice it forever hands apart and get it right, and as soon as I put them together I space on the position shift. So, I go back REALLY slow-glacially slow-and maybe get it right a couple of times, but then when I come back to it cold later on and try to play it through--dang it, I space on that shift again! It feels like none of the repetition is doing any good, although I should think it has to sometime.
Earlier I was having a dickens of a time on bar five, which begins with the original triplet figure (except starting with the ring finger in my edition) and continues into the next octave with the right hand. I've finally managed to work the kinks out of that one. Took a while though.
The common thread here seems to be that NO progress is possible without taking things real slow and deliberate, and just going over it and over it. My teacher says you can do that too much, but I'm not sure how much is too much. If I don't get it down, it doesn't make sense to just give up and move on, but that's usually what I end up doing anyway. I mean, I gotta sleep and eat sometime. And then there's this "w" thing that always gets in the way of my practice--unfortunately it pays my bills an mortgage, so I don't have much of a choice.
The progress I have made since January suggests that eventually I get over these humps. It just seem like it takes forever. Being the impatient type, I have my sights set on goals so far along down the road that the necessary steps along the way seem more like obstacles than the necessary means to getting there.