I think Old Chong helps Jing Mei because his approval is unconditional, even though (or because) his perception of what she is doing is limited by his poor hearing and sight. For Jing Mei, this is a welcome change from the constant criticism and nagging of her controlling mother, and allows her to determine her own destiny in this one small matter on her own. When she discovers that she can "be lazy and get away with mistakes, lots of mistakes", Jing Mei takes full advantage, and although she pays the price for her poor decision, still, it is her decision, and she has no one else to blame. I think that the opportunity which Old Chong unwittingly gives her to make her own mistakes allows Jing Mei to see the truth about herself more clearly, now that her vision is not clouded by frustration and resentment. She admits, "I really never gave myself a fair chance...I might have become a good pianist...but I was so determined not to try".