The students sat down for the filming expecting to hear specific business and money advice, the director says. “Instead, Warren told them tricks about life itself, and how to live a good life, how to have principles, and how to work hard and be patient.

“His entire class, which lasted for a couple of hours, was about how to become a good, decent person, and how by becoming a good and decent person, you will become a successful person in business as well.”

It’s a principle that his father instilled in him. “His father taught him to have an ‘inner scorecard,’ rather than an ‘outer scorecard,'” Kunhardt tells CNBC.

“An ‘outer scorecard,’ which many people have, is: What will people think of me? Will they judge me by the way I dress or the way I look or the car I drive?

“And the ‘inner scorecard,’ which is much more important, is: Am I doing the right things? Am I treating people correctly? Is this working for me as an individual?”

Focusing on an “inner scorecard” worked for the self-made billionaire. As Kunhardt says, “Warren believes that honesty has paid off from a business point of view much more than being sleazy or dishonest would have. He’s always taken the high road and it’s paid off well.”