I wish I could remember where I read this as it was a really helpful way of looking at things.
When you are at a plateau it may seem as if you are making no progress. Learning nothing. But while you are there is when you are learning the most and it is when you find the understanding and it becomes easy again that the lesson has been learned. That point of feeling stuck and trying and trying again to find the right "feeling" or answer, is when you are in fact making the most progress.
Makes plateau no less frustrating but at least more bearable.