Sales of television show DVDs have exploded over the past few years. But why do viewers shell out so much cash for what are essentially reruns? A study in the August issue of the Journal of Consumer Research suggests that “reconsumption,” as the researchers call it, is more complex than one might think. People use familiar entertainment to measure how their lives have changed in positive ways.

Cristel Antonia Russell, a marketing professor at American University, and Sidney J. Levy, a marketing professor at the University of Arizona, conducted interviews of 23 subjects, all of whom had recently “reconsumed” a book, movie or vacation spot. The researchers used open-ended questions to elicit long and descriptive first-person answers, then analyzed the transcripts for recurring themes and key phrases. The responses suggested that sometimes choosing to do something again was about reaching for a sure thing—the brain knows the exact kind of reward that it will receive in the end, whether it is laughter, excitement or relaxation. They also learned that people gained insight into themselves and their own growth by going back for a do-over, subconsciously using the rerun or old book as a measuring stick for how their own lives had changed. One woman, for example, rewatched the romantic Kevin Costner movie Message in a Bottle more than once: “It was helping her work through having an engagement that hadn't worked out,” Russell says. Every time she watched that movie, it reminded her of her own failed relationship—and her reactions helped her see she was getting over it.

“I was very surprised,” Russell says. “I thought that people reconsumed these things for nostalgia, to go back to the past. But they were actually very forward-looking and prospective.” What about the boredom factor, you might ask? There was none to speak of. After all, Russell says, paraphrasing Greek philosopher Heraclitus: You never cross the same river twice—it's not the same river, and it's not the same you.