What is tragedy of the commons?

The tragedy of the commons occurs when many users share a limited resource, and each user gains the full benefit of taking more while the cost is spread across all. Sensible choices for each person add up to a result that harms every person. The idea was popularized by the ecologist Garrett Hardin.

How it works

Each user sees a reinforcing loop: more use brings more personal gain. The shared resource has a balancing loop that regenerates up to a limit. When total use exceeds regeneration, the stock falls, and each user then works harder to keep the same income, which drains the stock faster. Solutions include rules on access, private or shared ownership with quotas, prices that reflect the shared cost, and feedback that makes the damage visible early.

The pattern applies well beyond pastures. Shared server capacity, a common support team, a joint marketing budget, and a public data pool can all be overused when each team bears only a small part of the cost.

Example

Say a pasture supports 100 cows without damage. Ten farmers each hold 10 cows. One farmer adds 5 cows, gaining 5 cows worth of milk while the grass loss is shared by all ten. All ten reason the same way, and 150 cows now graze. The grass cannot recover, and over time every farmer's cows produce less than before. This is an illustration with round numbers.

How to model it in Machinations

Model the shared resource as a Pool with a Source for regeneration limited by a Register. Draw each user as a Drain taking from the Pool at a rate they choose. Play the diagram with several users and chart the Pool, then add a quota Lever to see how it prevents depletion.