Apoorva Mehta had 20 failed start-ups before Instacart

The gig: Apoorva Mehta, 30, is the founder and chief executive of San Francisco grocery delivery start-up Instacart. Over the last four years, he has grown the company to more than 300 full-time employees and tens of thousands of part-time grocery shoppers. The start-up offers on-demand and same-day...