… is from page 134 of Deirdre McCloskey’s 1990 book If You’re So Smart: The Narrative of Economic Expertise:
The expert as expert, a bookish sort consulting what is already known, cannot by his nature learn anything new, because then he wouldn’t be an expert. He would be an entrepreneur, a statesman, or an Artist with a capital A. The expert critic can make these non-expert entrepreneurs more wise, perhaps, by telling them about the past. But he must settle for low wages. Smartness of the expert’s sort cannot proceed to riches.
Economics teaches this. What it teaches is the limit on social engineering. It teaches that we can be wise and good but not foresighted in detail. Economics has something to teach the humanities, if they happen to think they know the future of art. It has a lot to teach experts, if they believe in magic.