true i have only being playing paino for almost 2.5 years. And I skipped and reached grade 10 piano in 2.5 years, so maybe my fundamental skills is not good enough. I can play the song, and play it fast, but it is tire sometimes. I can play that part very fast if i started at that part but when i start in the begining, when i reached that fast part, my hand is already tired. It's more of a stima problem than a technique problem.