As costly as it was for American Express to lose Costco, it would have been more costly to retain Costco. As big a win as Costco is for Citibank and Visa, it’s a deal afflicted by the winner’s curse because Citi/Visa had to overpay to secure it.
But American Express lost 10% of its credit card portfolio overnight. And it signaled a huge change for the company’s business to Wall Street. It set in motion a huge set of changes at the company, at competitors, and in deals other banks made with other airlines.