Once a public good exists, everyone can benefit from it without paying a cent

A lighthouse, clean air or national defense all share a quirk: once they exist, nobody can be stopped from benefiting, whether they helped pay for them or not. Economist Mancur Olson formalized this 'free rider problem' in 1965, arguing it explains why groups often fail to provide goods that would benefit everyone — each person has an incentive to let others foot the bill while enjoying the result for free, and if everyone reasons the same way, the good never gets built at all.

— Mancur Olson, The Logic of Collective Action: Public Goods and the Theory of Groups — Harvard University Press, 1965