It is right or not that your skill is going to improve when you get a trough? I am not sure, " trough" is used properly at here. In my case, I was recently practising English hangwriting. I clearly remember that in some periods I can't write as well as the last day what I had done. And it is also in playing billiards, I had practised a kind of shooting, but next day or next hour I can't make it... Fortunately, I have had a bigger progress than the fall- back... I just found it... does not it make sense, or it means I am not hard enough in what I am doing, or just a kind of imagination?