Ms. Nopphan believes that homelessness is more intractable in rich societies. “In wealthy countries there are systems for everything,” she said. “You’re either in the system or out of the system.” There is no in-between in America. In Bangkok, by contrast, rich and poor coexist. There are vast tracts of cheap, makeshift homes and a countryside where people in the cities can return to if they lose their jobs or hit hard times.