There are many apparent reasons why people engage in activity, such as to earn money, to become famous, or to advance science. In this report, however, we suggest a potentially deeper reason: People dread idleness, yet they need a reason to be busy. Accordingly, we show in two experiments that without a justification, people choose to be idle; that even a specious justification can motivate people to be busy; and that people who are busy are happier than people who are idle. Curiously, this last effect is true even if people are forced to be busy. Our research suggests that many purported goals that people pursue may be merely justifications to keep themselves busy.