A country should trade even in goods it makes best, if the maths works out right

In 1817, economist David Ricardo showed that two countries can both gain from trade even when one is more efficient at producing everything, as long as each specialises in whatever it's relatively less bad at and trades for the rest. The insight, comparative advantage, remains the core argument for why free trade can benefit both sides.

— David Ricardo, On the Principles of Political Economy and Taxation — 1817