… is from page 13 of Steven Pinker’s 2018 book, Enlightenment Now :
Specialization works only in a market that allows the specialists to exchange their goods and services, and [Adam] Smith explained that economic activity was a form of mutually beneficial cooperation (a positive-sum game, in today’s lingo): each gets back something that is more valuable to him than what he gives up. Through voluntary exchange, people benefit others by benefitting themselves…. Smith was not saying that people are ruthlessly selfish, or that they ought to be; he was one of history’s keenest commentators on human sympathy. He only said that in a market, whatever tendency people have to care for their families and themselves can work to the good of all.