Sapiens by Harari covers this extensively. So much of human development is our ability to ascribe fictive boundaries and definitions to things. Rules, authorities, myths, money, culture, countries, companies. What are any of them? They're all made up. We could just stop believing in all of them tomorrow.

+1 for the Graeber quote. I wasn't familiar with it but makes sense he would have originated it. Dovetailing that with this Ask HN theme: When you realize that bog-standard consumer loan amortization formulae are arbitrary and not grounded in any fundamental reality more detailed than "the lender gets something in addition to the amount lent", it's eye-opening. I didn't really recognize that until after reading his Debt: The First 5000 Years (yes, I'm familiar with the statement flaws that others have commented before about his works), but set against alternatives I learned about in business school, like zero-coupon bonds (special to corporates, bondholders, and banks) it put the standard loan amortization schedule into context.