Local urban problems and the needs of small businesses are increasingly becoming inspiration for start-ups, and selling door-to-door — that icon of 1950s entrepreneurialism — is back with a new, digital face. Putting on a show for investors is one thing; facing off with an endless stream of bartenders and cash-register attendants over the shop counter is an entirely different proposition. Yet that’s exactly where many members of the newest crop of innovators are winding up as they try to bootstrap their billion-dollar ideas, one customer at a time.

Selling is where business happens. This is going to separate the simple nerds from the real entrepreneurs.