Bill Gates believes one trait sets him apart from most other people and helped him become so massively successful, he says: his rampant, rabid sense of curiosity.

"I put a lot of energy into trying to learn things," Gates tells CNBC Make It. That's perhaps an understatement: From a young age, Gates spent hours at a time reading deeply about a wide variety of topics, from computer science to history and climate change, he writes in his new memoir, "Source Code," which published on Tuesday.

At age 9, for example, Gates read the entirety of his family's World Book Encyclopedia collection, in an attempt to satisfy his insatiable curiosity. The attempt was a bit "silly," he now says: "You're reading all of the B's, and the C's, and then the D's and all that. Who knows how much of that I retained?"

Gates has sought "a broad set of knowledge" throughout his life and career, and his open-minded curiosity has been a crucial ingredient in his success, he says. Rather than only focusing on math and computer science classes during his three semesters as a Harvard University undergraduate, Gates loaded up on extra classes that interested him, like criminal justice and British history.

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Psychology courses were "valuable" for his still-developing social skills, he says, while economics courses proved useful when he went on to run one of the world's largest businesses.

"I got to use almost all of the knowledge that I acquired, and I was glad that I had the curiosity to take all of those different courses," says Gates. "So, I'm always encouraging people to learn a broad set of things."

When Gates later stepped down as Microsoft CEO in 2000, he looked for other ways to occupy his time and money. His reading on global health crises, climate change and other non-software topics helped inspire the philanthropic pursuits that now take up much of his energy and focus, he's said.

Curiosity 'requires nurturing'

Gates is glad he grew up before the constant distraction of smartphones and social media, he's said — but he's still envious of the information that modern kids have at their fingertips.

"It's easier to learn things today. The stuff that's online is just so miraculous," says Gates. "I used to have to go and dig around the library and find different books."

His family supported his intense curiosity, even when he'd disappear to his room for hours to read, sometimes only emerging to pepper his parents' friends and colleagues with questions when they visited the Gates' home, he writes in "Source Code."

Gates' parents frequently invited people for dinner parties and group discussions, from local politicians to lawyers who worked with Gates' attorney father, and his mother encouraged a young Bill to take part and learn from their adult guests. Other times, Gates' father let him pore over the lawsuits and legal filings he was working on, teaching him about the inner workings of the law.

"Curiosity can't be satisfied in a vacuum, of course. It requires nurturing, resources, guidance, support," writes Gates.

Gates credits his parents for taking his inquiries seriously, encouraging dialogue and praising him for asking more and more thoughtful questions, he says: "It's a pretty amazing way that [they] took whatever my natural predilection was and really pushed it forward."

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