Who is your competition? It may not be who you think it is. I was reminded of this again recently as I read a Knowledge@Wharton interview with MasterCard CEO Ajay Banga. You might think MasterCard’s competition would be American Express or Citibank – no, Ajay says their competition is cash.

As Banga explained, 85% of the world’s transactions are conducted using cash. He asserts that to focus on his traditional competitors means wrestling with them for 15% of a global market. He’d rather go aft...