… is from page 157 of Deirdre McCloskey’s superb 1990 book, If You’re So Smart: The Narrative of Economic Expertise (original emphasis); Deirdre here is discussing the late Lester Thurow’s 1986 book, The Zero-Sum Solution, a book in which Thurow used sports metaphors to make the mistaken case that international trade is a competition among nations:
The subject, though, is the exchange of goods and services, Japanese automobiles for American timber, German steel tubes for Soviet natural gas. The game metaphor does not seem apt. If exchange is a game it resembles one in which everyone wins, like aerobic dancing. Trade in this view is not zero sum. It is positive sum. There are social, overall, mutual gains from trade. How does an economist know? Because the trade was voluntary.