It is imprudent for a man to make what is cheaper for him to buy. A naive man might find the constituent parts of his trainers cost less than a pair from JD. In reality, economies of scale mean this probably isn’t true, but let’s pretend it is. The missing cost is the time it would take to acquire the knowledge to build the shoes and the many hours he’d spend trying. These are not negligible costs. We buy t-shirts we could possible make ourselves because we have better things to do with our time. As a developer, I’m better off sticking to coding, making money, and using it to buy the items that would take me an age to produce.

If this is true within a country, it’s also true between countries. Another nation that can more efficiently produce steel should do so. We should benefit from it by sticking to our comparative advantage and using part of the proceeds to buy what we need internationally. Arguments about labour displacement and wage decreases obfuscate the fundamental point that trade is a positive sum interaction. For every loser that ends up with a lower salary, there are thousands of winners who pay less.