<COMMON POOL RESOURCES>

•  "Overfishing is 'catching fish faster than they can reproduce,' depleting stocks and damaging marine ecosystems by disrupting food webs, reducing biodiversity,..." 

 "So how do we show overuse on a diagram?" 

• Well, from the last 'THINK AHEAD' you should have realised that the usage of these 'natural resources' are part of the productive process, and therefore when they are consumed to an extent that creates costs for others (e.g., so much pollution that it creates healthcare costs), then THIS OVERUSE CAN BE GIVEN A MONETARY VALUE' to reflect this 'EXTERNAL COST TO SOCIETY' that has been created as a consequence of this overuse and more crucially a cost that society HAS NOT RECEIVED ANY COMPENSATION FOR by the producer. 

• In other words it is NOT FACTORED into the producers costs of production when they determine their supply curves, implying that in fact there exist TWO supply curves, one reflecting the producers private costs ('Private cost curve'), and one including these private costs plus the additional external cost ('Society's supply curve')

• "So what?", Well if you think about it TWO SUPPLY CURVES implies TWO EQUILIBRIUM QUANTITIES. 

• If this EXTERNAL COST was given a $$$ value and ADDED TO THE FIRM'S PRIVATE COSTS, then their SUPPLY CURVE WOULD SHIFT TO THE LEFT and output would fall accordingly. 

• Hence we can say that the MARKET HAS FAILED to include ALL COSTS and hence has FAILED to deliver the SOCIALLY OPTIMAL ALLOCATION OF RESOURCES.

"In school you are moved from classroom to classroom for each subject, so keeping the classroom clean and tidy is not your top priority, as you barely spend time there, leading to gradual deterioration, but do you think you would look after the classroom better if you had your own desk and teachers came to you rather than the other way around?"