From Cosma Shalizi's fable on Pareto optimality and economic efficiency:
And so, in yet another triumph, the market mechanism has allocated a scarce resource, viz., the turkey, to its most efficient use, viz., being turned into artificial shit. What makes this the most efficient use of the scarce resource? Why, simply that it goes to the user who will pay the highest price for it. This is all that economic efficiency amounts to. It is not about meeting demand, but meeting effective demand, demand backed by purchasing power.