The story of Warren Buffett, the "Oracle of Omaha" and legendary billionaire investor behind Berkshire Hathaway, is practically universally known. Yet his business partner, Charlie Munger, is arguably lesser known.

The two men met back in 1959, when both men worked at the Nebraska grocery store owned by Buffett's grandfather. From there, a friendship developed and Munger has been Buffett's right-hand- man at Berkshire Hathaway since 1978. The 88 year old Buffett serves as chairman, while 95 year-old Charlie is vice chairman.

So how does a partnership that spans decades work for that long? Munger recently told CNBC's Becky Quick that the secret to a long and happy life is "easy, because it's so simple." His advice applies to both business and the personal.

"You don't have a lot of envy, you don't have a lot of resentment. You don't overspend your income, you stay cheerful in spite of your troubles," the Berkshire executive said.

"You deal with reliable people and you do what you're supposed to do. And all these simple rules work so well to make your life better. And they're so trite," Munger added.

And how old was he when he figured out these "simple rules"? He replied: "About seven."

Munger explained that even at that tender age, he could see that some "older people were a little bonkers." He said ability to recognize that "always helped me because there's so much irrationality in the world."

Munger added that he's thought about the "causes and preventions" of irrationality "for a long time." As a result, he found that "staying cheerful" has helped him in life "because it's a wise thing to do."