Today, psychologists, economists and environmentalists use the phrase “the tragedy of the commons” to describe the same basic principle: when we use a common resource at a rate that is slower than the rate at which it replenishes, all is well. However, if a few individuals get greedy and use more than their share, the system of consumption becomes unsustainable, and in the long term, everybody loses. In essence, the tragedy of the commons is about two competing human interests. On one hand, an individual should care about the sustainability of shared resources in the long term because everyone, including the individual, benefits from it. At the same time, in the short term, the individual benefits immediately from taking more than his or her fair share. (Social scientists refer to such betrayers of social contracts as “defectors.”) Of course, if we all cared about the common good or thought about the long-term consequences of our actions, we might not run into resource-sharing problems. But because human beings tend to focus on short-term benefits and our own immediate needs, such tragedies of the commons occur frequently.

– Dan Ariely