I remember George Leonard sensei writing in his book Mastery that everyone must undergo plateaus in their learning and that these plateaus are necessary in their progress. As he says, in order for a golfer to break 90 strokes in his game, he'll probably have to play up in the 100's for a while. Breakthroughs never happen on their own but are results of being on those plateaus.
I think that dealing with frustration is very much part of the training process. If it were all honey and cream without discomfort, we wouldn't be learning anything...