I used to spend months and months on one etude to try and force it to work, but honestly it just led to more and more frustration. I remember spending an entire semester in Grad school on one etude (and other things as well), and getting to the end of the semester and my teacher saying, it has improved, but your articulation is still not consistent from one note to the next. It frustrated me, but I had learned something.
Etudes, and music in general are not about being able to play it perfectly within a day or a week, but learning and improving through working on it for a certain amount of time. Recently, I came back to an etude that I had been initially assigned to work on 2 years ago. At that point, I couldn't even get through the whole etude even after working on it for a few weeks. Well, I've picked it back up, and can now play through the entire etude after a few weeks of working on it. However, it is still quite under tempo, the articulation is not as steady and clean as I would like, and my breath is taking up too much time.
But I'm not going to beat this one particular etude into the ground, I recorded it today, and sent it to a friend for feedback or just to listen to. These individual aspects of playing can be worked on through other means. I can pick an etude, such as a Vurm or Reynolds, that really works on playing steady 8th notes, or I can play simple melodies or pick solos that force me to breath quickly in time.
This one etude does not have to be perfect before I move on. In fact, it never will be "perfect." There is no arrival, merely process. I am grateful to have improved since the last time I worked on the etude, yes there is progress, but I can work on the things that need more improvement in other settings.
Time to Keep Exploring,
Adam