Covid-19 has shined a spotlight on many of the world's networks, from the internet to international air travel. But the supply chains that crisscross the world--the ships and trucks and trains that link factories to ports and warehouses, bringing almost everything we buy many thousands of miles from where it's produced to where it's consumed--are facing more scrutiny than they ever have. "It's fair to say that whatever you're selling, you've got a problem right now," says Jason Boyce, founder and CEO of Avenue7Media, a consulting firm that advises top Amazon sellers. Boyce says he has clients who would be turning over tens of millions of dollars a year if they could stay in stock. "We're having talks with clients every day where they're just crying," he says.