Every day for a month, Praise Olaoluwa showed up at Eko market, the cluster of Balogun and Idumota markets on Lagos Island, one of Nigeria’s commercial hubs. Not to sell anything. Not to pitch anyone. Just to be there – to eat lunch with the traders, share dinner, celebrate birthdays, buy a bottle of whisky when someone added another year. He was trying to understand how these businesses breathed: how they bought, how they sold, and how money moved through their hands each day. Then he noticed something. Every time he showed up, someone asked the same question, almost jokingly: “Have you come with money for us?” It happened once. Then again. And again. Different traders, the same question. “It didn’t happen once. It didn’t happen twice,” Olaoluwa says. “There were different people who...