At the Equilibrium Quantity There Are no Unexploited Gains from Trade or any Wasteful Trades
Panel A: Unexploited gains from trade exist when quantity is below the equilibrium quantity. Buyers are willing to pay $57 for the 24th unit and sellers are willing to sell the 24th unit for $15, so not trading the 24th unit leaves $42 in unexploited gain from trade. Only at the equilibrium quantity are there no unexploited gains from trade.
Panel B: Resources are wasted at quantities greater than the equilibrium quantity. Sellers are willing to sell the 95th unit for $50, but buyers are willing to pay only $15 so selling the 95th unit wastes $35 in resources. Only at the equilibrium quantity are there no wasted resources.
Panel A: Unexploited gains from trade exist when quantity is below the equilibrium quantity. Buyers are willing to pay $57 for the 24th unit and sellers are willing to sell the 24th unit for $15, so not trading the 24th unit leaves $42 in unexploited gain from trade. Only at the equilibrium quantity are there no unexploited gains from trade.
Panel B: Resources are wasted at quantities greater than the equilibrium quantity. Sellers are willing to sell the 95th unit for $50, but buyers are willing to pay only $15 so selling the 95th unit wastes $35 in resources. Only at the equilibrium quantity are there no wasted resources.