In the short story “Rules of the Game” by Amy Tan, what motivates the narrator to excel at chess?

The thing that had motivated her in the beginning to keep winning was the gummy candies the narrator and her brother used as replacements for missing chess pieces. The winner would get to eat them, and she would lose to her brothers the first few times, so she practiced to beat them and keep the candy.

i would think its the desire to gain invisible strength.