Rose flips to a week in April and notices three entries. "There will be four, maybe, by April," says Buffett.

"It's very high tech, be careful, you might not understand it," Gates jokes.

"I also remember Warren showing me his calendar," says Gates. Buffett hands his little book to Rose to examine. "There's nothing on it," says Rose, flipping through the book.

Rose asks Gates what he has learned from Buffett. First, he learned that it's "not necessarily a good idea to leave large sums to your children," says the Microsoft co-founder. And then there was the little paper appointment book Buffett showed Gates .

"It's the only thing you can't buy. I mean, I can buy anything I want, basically, but I can't buy time," the "Oracle of Omaha" says in a 2017 conversation with his billionaire buddy Bill Gates , hosted by Charlie Rose.

With more than $88 billion to his name , there isn't much Warren Buffett couldn't buy. Except, as the now 88-year-old CEO and chairman of Berkshire Hathaway is keenly aware, there is one thing his fortune won't help him get more of: time.

"You know, I had every minute packed and I thought that was the only way you could do things," says Gates. But, he says, Buffett taught him the importance of giving yourself time to think.

"You control your time," says Gates. "Sitting and thinking may be a much higher priority than a normal CEO, where's there all these demands and you feel like you need to go and see all these people. It's not a proxy of your seriousness that you fill every minute in your schedule."

"I better be careful with it. There is no way I will be able to buy more time," says Buffett.

Billionaire serial entrepreneur Richard Branson agrees: He believes that being intentional about taking time away from your to-do list helps you set ambitious goals.

"Open your calendar and schedule time just to dream," recommends Branson in a post he wrote on his blog in 2017.

"Put it in your diary like you would a meeting. Far too many people get weighed down in doing, and never take the time to think and feel. Take five minutes, an hour, a day, or even a holiday. If you free up some time to think freely, you'll be able to see the bigger picture much easier," Branson says.

Emma Seppälä, the science director of Stanford University's Center for Compassion and Altruism Research and Education, co-director of wellness at Yale Center for Emotional Intelligence, and author of "The Happiness Track: How to Apply the Science of Happiness to Accelerate Your Success," says her research shows that Buffett and Branson are onto something.

"From Vincent Van Gogh on through Kanye West, the figure of the broody, tortured artist looms large in the popular imagination. But research suggests that the key to creativity has little to do with angst. In researching my book 'The Happiness Track,' I found that the biggest breakthrough ideas often come from relaxation," says Seppälä in a piece for Quartz in 2017. "History shows that many famous inventors have come up with novel ideas while letting their minds wander."

Being constantly occupied doesn't give our minds time to think in new ways, she says. "Simply put, creativity happens when your mind is unfocused, daydreaming or idle. (This is why we have so many "aha" moments in the shower.)"

In other words, your next break from the inbox may be the most productive time you spent all day.

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