"Like everybody, I wondered how this experience would help me personally with my finances. What lesson am I going to learn that's going to make me rich like Warren?" Kunhardt told CNBC. "There is no answer to that. Warren is as successful as he is because of a combination of his unique brain and the principals that his father and family instilled in him."

Within a week, Kunhardt received a reply from famous investor Warren Buffett saying yes. The Emmy Award-winning producer made " Becoming Warren Buffett " between 2014 and 2016, after five visits to Omaha, where Buffett resides.

When filmmaker Peter Kunhardt asked friend Peter Buffett if his dad would be open to him making a documentary out of his life, Buffett told Kunhardt to write him a letter.

That being said, "there is one thing that we can all do like Warren" when it comes to investing, Kunhardt said: Be patient.

"He feels that once you connect with a company that you like — a company that you believe in — you should stick it out for the long haul," the producer says of Buffett's investing strategy. "And that's what he's done. He buys stocks for life. Unless something dramatic happens that changes his mind, he can live through the ups and downs because he knows that at the center of it is a healthy company that he believes in."

Buffett only invests in companies that are within his "circle of competence," a concept he first described in his 1996 Shareholder Letter: "You don't have to be an expert on every company, or even many. You only have to be able to evaluate companies within your circle of competence. The size of that circle is not very important; knowing its boundaries, however, is vital."

Simply put, stick to what you know. "Defining what your game is — where you're going to have an edge — is enormously important," Buffett tells Kunhardt in the documentary. Once you've done that, buy and hold for the long term.

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