Ranjay Gulati, professor at Harvard Business School, says the most successful organizations tend to have one thing in common: a soul. Moving beyond culture, the "soul" of a growing start-up -- or a more established company -- is built on clear business intent, a strong connection to customers, and a stellar employee experience. Gulati says that leaders must think hard about preserving all three elements of the soul even as they scale and never lose sight of what makes their company special. He's the author of the HBR article "The Soul of a Start-Up."