A man who's interviewed Bill Gates and Richard Branson says you need this skill to be successful

Bill Gates at the 2015 CGI Annual Meeting in New York
Adam Jeffery | CNBC

In today's world, it's easy to have your attention pulled in different directions. But if you want to be successful at a young age, there's one skill you must master: focus.

That's according to success expert Richard St. John, who has interviewed over 1,000 successful people including Bill Gates, Richard Branson and Martha Stewart. In 2005, he gave one of the most watched Ted Talks ever, "8 Secrets of Success," which has been viewed more than 10 million times.

"Focus is the big one," St. John tells CNBC Make It. "Focus is the secret to most people's success." People who concentrate are the ones who become successful at a young age, he says.

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St. John says that when you're young, it's okay to initially dabble in a few things. But there comes a time when you need to "just pick one thing," and it should be something you're passionate about.

This, he says, makes focusing not seem like a chore. In his interviews with highly successful people and billionaires over the last 10 years, St. John says they rarely get excited discussing money. It helps that they have some, he says, but it's never the focus.

"But when you talk about their passion, they light up," he says.

St. John says successful people hate moderation, which helps them to channel their focus. "It's all or nothing," he says. He notes that there is a major distinction between concentration and focus.

"Concentration is being able to get something done in the short-term," explains St. John. Focus, meanwhile, is paying attention to one thing long-term.

Most importantly, say St. John, successful people are not jacks-of-all-trades.

"Successful people aren't great at everything," says St. John. "They are great at one thing and suck at everything else. If you focus on too many things, you won't be able to spend time on what makes you great."

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