What is the theme in Something Blue by Emily Giffin?

Competition is a theme in the story. Darcy is competitive even as a child. Due to her mother's coaching, Darcy believes beauty is her avenue toward popularity and success. Contrary to what Darcy professes, competition doesn't stop with her best friend. Rachel is plain in looks but superior in intelligence. As a child in fifth grade, Darcy becomes jealous when Rachel is promoted to a gifted class. Therefore, Darcy belittles her friend's success. When Darcy finds out Rachel has a crush on Ethan, Darcy decides she likes him, too. At first, Darcy says she hopes Rachel will be happy they like the same boy, but when Rachel instead professes her claim on Ethan, Darcy decides to ask Ethan to be her boyfriend.