one of the most famous idioms of the novel:

"Wise guy, he not go against wind. In Chinese, we say, Come from South, blow with wind--poom!--North will follow. Strongest wind cannot be seen."

This idiom is clear to Waverly, but what does it mean? Basically, the Chinese believe that requests must be accompanied by dignified speech. In fact, losing one's temper is very bad form and unlikely to bode well in any type of negotiation scenario. Knowing the strength and weaknesses of one's adversary, however, gives one an advantage. In this conflict, Waverly's mother has the upper hand. After all, she is the parent.

Waverly would have served her cause better by asking for the bag of plums courteously. Of course, there is no guarantee that her mother would have acquiesced to her demands, even if Waverly had asked politely. However, there is a high likelihood that Waverly's request would have been received with greater charity. As a result, a successful future outcome would have been more likely.

This interesting idiom teaches Waverly the importance of knowing the strengths and weaknesses of one's adversary. We may not be able to overcome a stronger adversary by conventional means, but we can use any acquired knowledge about our adversary to our advantage.

In this case, Waverly should have understood that she would never be able to move her mother (an "adversary" with a stronger will) by resorting to emotional theatrics. Later, after Waverly learns to "bite back" her tongue, her mother surprises her by purchasing the coveted bag of salted plums.

When Waverly cries to get a bag of salted plums, her mother, Mrs. Jong, scolds her.  She does not give in for a moment.  In fact, she says: “bite back your tongue.”  This incident comes directly after Waverly’s recounting of her mother’s lessons about the art of invisible strength.  According to Waverly, this art was used to win arguments and respect from others. In light of this, we can say Mrs. Jong was teaching her about how to live life well and how to succeed.

From this perspective, this incident, though small, was actually profound in shaping Waverly.  That this lesson worked can be confirmed, because there is another plum story that follows.

Waverly and her mother were at the store again. It can be assumed that Waverly still wanted the salted plums, but this time she did not cry or throw a tantrum. When Mrs. Jong saw this, she bought a bag of plums for Waverly.

While she's shopping at the store with her mother one day, Waverly asks for a bag of salted plums. But her mother refuses to buy her one. It's not that she's being cruel or vindictive; she just wants her daughter to exercise self-control, which she believes is a necessary precondition of achieving success in life. Nevertheless, whatever her motives, Mrs. Jong angrily scolds Waverly, telling her that, in future, she should learn to bite her tongue in order to control herself.

Whether or not this is the right approach for a parent to take in such circumstances, it seems to work. The next time Mrs. Jong and Waverly go shopping, Waverly doesn't ask for any plums. This tells Mrs. Jong that her daughter has matured and learned her lesson. As a reward for Waverly's self-control, Mrs. Jong quietly plucks a small bag of plums from the rack and puts it on the counter with the rest of the items she's bought.

In the beginning of the story, Waverly cries to get a bag of salted plums. Her mother does not give in to her plea as a dotting parent.  She does not buy the plums for her.  Instead, she scolds her, and she says that Waverly should bite back her tongue. This incident takes place right after Mrs. Jong tries to teach her daughter the art of invisible strength.  

In light of this close connection, it seems that Mrs. Jong was trying to teach her daughter to control herself and her emotions.  If she could do that, she will have strength to succeed in life. Here is the quote:

"Bite back your tongue," scolded my mother when I cried loudly, yanking her hand toward the store that sold bags of salted plums. At home, she said, "Wise guy, he not go against wind. In Chinese we say, Come from South, blow with wind-poom!-North will follow. Strongest wind cannot be seen."