Driving down prices and forcing suppliers to be more efficient is great for consumers, of course, and indeed it has benefits for the wider economy—a McKinsey study made the extraordinary finding that Walmart alone was responsible for 12 percent of the US economy’s productivity gains in the second half of the 1990s.5 But for suppliers, it makes life difficult. If a harvest fails and the costs of production go up, you can bet that it is the farmers, not the supermarket or its customers, that will be made to feel the squeeze.
