So when 16-year-old Jeff got a summer job frying up burgers at McDonald's in 1980, he learned all he could from the experience.

"I knew early on that he was wired a little bit differently," she says. "When he tried to take his crib apart with a screwdriver, I think that cinched it."

Amazon CEO and self-made billionaire Jeff Bezos was always unique, even as a kid. His mother Jacklyn, who became became pregnant with Bezos at 16 , remembers his fascination with discovering the way machines and toys worked.

"I was a cook," Bezos told Fast Company. "They wouldn't let me anywhere near the customers. This was my acned-teenager stage. They were like, 'Hmm, why don't you work in the back?'" he joked.

As a "grill man," the most challenging thing for Bezos "was keeping everything going at the right pace during a rush," he told Cody Teets, author of "Golden Opportunity: Remarkable Careers That Began at McDonald's."

The experience was Bezos' first hands-on brush with retail, according to Wired, and he spent the summer "studying the company's automation improvements," like beeps and signals for when to "scramble his eggs, flip his burgers, and pull his fries out of the boiling vat."

The job also gave him early insight into customer service: "I learned that it's really hard," he told Fast Company. Today, "customer obsession" is the first one of Amazon's leadership principles.

Bezos isn't the only entrepreneur to glean lessons from working at a fast-food chain. Reddit co-founder Alexis Ohanian was a waiter at Pizza Hut in high school, after working his way up from a dishwasher.

As a waiter, "I learned basically everything I've ever needed to know about customer service," Ohanian told The New York Times.

Barbara Corcoran, star of ABC's "Shark Tank, found similar value working as a waitress in her early 20s.

"You learn more in waitressing than you can in any other job," Corcoran tells CNBC Make It. "The best job you could have to prepare for entrepreneurship is, walk on the other side of the counter and serve people."

As for Bezos's time at McDonald's, his advice for young people is to always keep your eyes open for lessons to learn at any gig, even it's just flipping burgers.

"You can learn responsibility in any job, if you take it seriously," he said in "Golden Opportunity."

"You learn a lot as a teenager working at McDonald's," he said. "It's different from what you learn in school. Don't underestimate the value of that!"

Don't miss: Here's why Jeff Bezos still drove a Honda long after he was a billionaire

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