On October 31, 2009, Microsoft pulled the plug on MSN Encarta, its disc and online encyclopedia, which had been on the market for sixteen years. Meanwhile, Wikipedia—that second model—ended up becoming the largest and most popular encyclopedia in the world. Just nine years after its inception, Wikipedia had more than 17 million articles in some 270 languages, including 3.5 million in English alone.1 What happened? The conventional view of human motivation has a very hard time explaining this result.
