"Digital-commerce sales worldwide are expected to hit $4 trillion by 2020, about double of where it is now," according to a report published in the Harvard Business Review. "A major hurdle is the continuing stickiness of cash, which has not been displaced by digital alternatives despite myriad options."  Consider today's digital landscape: Digital technology is widespread and spreading fast. Digital players wield outsize market power. Digital technologies are poised to change the future of work. Digital markets are uneven. Digital markets must still contend with cash. Click for report