The "tragedy of the commons" is an idea put forward by Garrett Hardin in the late 1960's (http://en.wikipedia.org/wiki/Tragedy_of_the_commons), describing how commonly held resources are supposed to be stripped to nothing when those who use them act solely on self-interest instead of in the common good. The notion is that a community resource will be over-used when individuals apply their private profit calculation to how much of it they will employ.
