Rob Gordon (John Cusack) is a self-confessed music loving everyman with a poor understanding of women. After getting dumped by his latest girlfriend, Laura (Iben Hjejle), he decides to look up some of his old partners in an attempt to figure out where he keeps going wrong in his relationships.
He spends his days at his record store, Championship Vinyl, where he holds court over the customers that drift through. Helping Rob in his task of musical elitism are Dick (Todd Louiso) and Barry (Jack Black), the "musical moron twins," as he refers to them. Armed with an encyclopedic knowledge of all things musical, they compile "top five" lists for every conceivable occasion, openly mock the tastes of their customers, and, every so often, sell a few records.
Rob and the staff have a strong dislike for two shoplifting skateboarder teenagers, Vince (Chris Rehmann) and Justin (Ben Carr). One day, he listens to a recording that they made and offers them a record deal, starting his own label called Top 5 Records. During his off hours, he pines for Laura and does his best to win her back.
Rob soon hears that Laura's father, who liked Rob, has died, and attends his funeral with Laura. Shortly after the reception, Rob realizes he never committed to Laura and always had one foot out the door. This made him realize he neglected his own future in the process. Afterward, he and Laura move back in together again. Rob meets a music columnist whom he soon develops a crush on, but while making a mixtape for her, wonders if he'll always just be jumping rock to rock. Laura meets with Rob in a bar where he explains how other girls are just fantasies, and while Laura is a reality, he never gets tired of her. He then proposes marriage to her, and she thanks him for asking. Later, she organizes an evening where he has the opportunity to revisit a love of his youth: dee-jaying. It is also a celebration of the recently released single by the two delinquents, where Barry's band plays "Let's Get It On". Surprised that Barry's band is not a disaster, Rob holds Laura, and they both sway to the music. Rob makes a mixtape for Laura, feeling like he's finally learned how to make her happy.

Question: Why did Rob Gordon look up his old partners?
Answer: To figure out where he keeps going wrong in relationships.
Alternative answer: to learn why his relationships kept failing