#system #game-theory #systemic-failure #policy #unintended-consequence


Tragedy of commons depicts a situation where system agents share a resource, and through the collective overuse of the resource (often marginally), spoil it for everyone ; while a reasoned use of the resource would ensure its durability.

It is a classic game theory problem where collaboration wins for everyone, and individuality loses for everyone.

The common example is overuse of pastures: if every shepherd only brings one cow to the pasture, then it will renew enough for the system to be durable. The shepherds get enough milk, so the situation is ok. If one shepherd brings one more cow though, the overuse is marginal and the system stays durable. Other shepherds seeing that, they fear being cheated, and all will soon bring a second cow, at which point the pasture will be overused, and cows won't have enough to feed.

This example depicts a system with two equilibrium: one that is desirable and profits everyone, but is local and instable. The other one which gets everyone's demise but is stable and natural. Therefore without additional policy, the system will almost certainly always end up on the undesirable state. That's the tragedy of commons.


Traffic congestion is an example of tragedy of commons