Everyone wants the lighthouse built. Nobody wants to be the one who pays for it.

Paul Samuelson formalized why goods like national defense or clean air are chronically undersupplied by free markets: once they exist, nobody can be excluded from enjoying them, so everyone has an incentive to let someone else pay and 'free ride' on the result. His 1954 paper became the founding text of public goods theory, still used to justify taxation for shared infrastructure.

— Paul A. Samuelson, The Pure Theory of Public Expenditure — Review of Economics and Statistics, 1954