Kyle MacDonald started with a red paperclip and ended up with a house. Trade and barter requires a double coincidence of wants, but Kyle was able to find people willing to give up something he valued more than his holdings. Mutually beneficial exchange makes both parties better off. This is a great clip to start the process of discussing why trading can grow an economy and why centrally planned economies are harder to coordinate.
Thanks to @AlcovyEconomics on Twitter for the clip!