Scott Cook has been studying businesses for decades, first while earning his Harvard M.B.A., later as a Procter & Gamble brand manager and consultant at Bain. And, of course, then as the founder of the hugely successful personal finance software company Intuit.

Over the course of his career, he's watched as the the requirements necessary to be a true leader have changed significantly. According to Cook, these days the mark of a great CEO has to do with your ability to retain your most valuable employees. Unlike a generation ago, when workers frequently stuck with one company for the majority of their careers, if not their entire career, now people switch jobs frequently, Cook says.

"[When it comes to] the skilled professionals, the people who have the brains in entrepreneurship to make a big difference, lots of companies want them," he says.

"There's almost a constant employment demand for the people who can really make a difference, so that means as a leader, not only are you trying to win the loyalty of your customers, you're trying to win the loyalty of your employees--and constantly re-win it--and earn their dedication and their enthusiasm."

Winning over your employees' loyalty won't just keep them at your company, Cook says, it will also inspire them to be "massively more creative and inventive."

The alternative, he says, is losing your best people.

To hear more about the changing nature of leadership, watch the video below.