Piano is for fun

上钢琴课上，老师说这个曲子回家你练的时候要好好数拍子。
小菜叹了口气，实话实说：
--I don't like counting when I am playing it.
老师说：
--You have to. If you don't count, you may get into trouble when you play it.
--Ah?
小菜吓了一跳：
--I think playing piano is for fun. How come I'll get into trouble?