This is Bart. Bart likes to fish, and maybe he likes it a little too much. Everyday Bart goes out to the ocean near his village to catch fish for his store. Bart takes at least 500 fish a day!
Other fisherman along with Bart are trying to catch enough fish to benefit themselves. At the same time the mass amount of overfishing is leading to a disruption in the ecosystem. Fish are being caught faster than they can reproduce.
This situation would be described as "tragedy of the commons". The actions are benefiting certain people and individuals, but in the long run effecting the large group that also depends on that resource. In this case, Bart overfishing is causing a problem for the ecosystem and others trying to fish in the region.