It means you are learning. In learning we improve. Yes, it still is frustrating because at the time it seems like you are getting no where. But once you get to the top of peak you feel the exhileration of your hard work.
But realize soon after you will be heading down the peak into another valley.
I believe the best way to deal with cycle is to realize that until you "master" aikido you will always have peaks and valleys. Just accept it as part of your training. That is what I did. If you get stuck on a plateau, then worry.
The analogy of turning a cube into a sphere is great, too.
Anne Marie Giri