Comparative advantage

This idea has been called one of the most profound insights in economics. If country A can make cars more cheaply than country B, and B can produce shirts more cheaply than A, it clearly makes sense to trade. Each has an absolute advantage in one area. But what if A is more efficient at producing everything than B? It still makes sense for them to trade, with B producing the goods where it is more competitive; if for example it is 90% as efficient as A in making shirts, and only 60% in car manufacturing, then it should specialise in making shirts and trade them for cars. Both countries will gain.