Managing rapid growth is a huge challenge for young businesses. Even start-ups with glowing reviews and skyrocketing sales can fail. That’s because new ventures and corporate initiatives alike must sustain profitability at scale, according to Harvard Business School senior lecturer Jeffrey Rayport. He has researched some of the biggest stumbling blocks to long-lasting success and he explains how to successfully transition out of the start-up phase. Rayport argues that success has a lot to do with an organization’s cash flow and its ability to meet growing demand. But it also involves something he calls “profit market fit,” which is when an enterprise becomes financially sustainable.