It refers to a question Matty asks his buddy: "How do you know... when you're in love or when he or she is the right person?" Likely a reference to the song, "How Do I Know if He Really Loves Me?", although I don't recall hearing that particular song in the movie.
Lisa, George, Matty, Charles, Annie, Al, Coach Sally, and Psychiatrist
What is the plot of How Do You Know?
After being cut from the U.S.A. softball team and feeling a bit past her prime, Lisa finds herself evaluating her life and in the middle of a love triangle, as a corporate guy in crisis competes with her current, baseball-playing beau.
What was the budget for How Do You Know?
$120 million
How much did How Do You Know earn at the worldwide box office?
$48.7 million
How much did How Do You Know earn at the US box office?
$30.2 million
What is How Do You Know rated?
PG-13
What genre is How Do You Know?
Comedy, Comedy Drama, Drama, Romance, and Romantic Comedy
