Why does the invisible strength Waverly learns from her mother help her at chess in "Rules of the Game" by Amy Tan? What is this strength?
The invisible strength Waverly learns from her mother helps her at chess because it allows her to hide her true power from her nemesis. In the story, her mother asserts, "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 just means every wise warrior is able to present a neutral exterior while hiding the depth of his power (and his weaknesses) from his enemies. According to Waverly's mother, the strongest winds cannot be seen; since all "weaknesses and advantages become evident to a strong adversary," the wise chess player must be discreet about her own strengths and weaknesses.
She must understand the "endgame before the game begins." If she is up against a superior force, she doesn't "go against the wind." Instead, she studies how she can use her opponent's apparently superior force to support her own ends and overcome him. If we remember the wind imagery Waverly's mother uses, we can conclude that:
A little knowledge withheld is a great advantage one should store for future use. That is the power of chess. It is a game of secrets in which one must show and never tell.
Essentially, the consummate chess player is able to hide her strategy from her opponent until she is able to "show" her strength through devastatingly shrewd moves.