There's a simple reason Leno has always had multiple streams of income, he says : "I had two jobs because I realized that was the quickest way to become a millionaire."

A few years later, when he was trying to break into the comedy scene, Leno supplemented his comedy gig earnings with money he made working at a car dealership.

His first two jobs were at McDonald's, where he sliced potatoes , and at a Ford dealership, where he worked as a the "lot boy," he tells CNBC Make It . "I would alternate between the two, so it was cars and hamburgers, which are actually still two of my passions."

From the moment comedian Jay Leno entered the working world as a teenager, he always had at least two ways to make money.

It wasn't just having two streams of income that would end up making him a multi-millionaire — it was how he handed both paychecks: He banked the bigger one and lived off the smaller one. When he was first starting out, that meant saving the money he made working at the dealership and spending what he made as a comedian.

"Then I got to the point where the comedy money was, like, five times the other money, so I decided to flip it around and save the comedy money," Leno says. "I would always spend the lesser amount of what the two were."

He continued relying on this strategy even after he started hosting "The Tonight Show" in 1992, which reportedly earned him as much as $30 million a year at the height of his career. "When I got 'The Tonight Show,' I always made sure I did 150 [comedy show] gigs a year so I never had to touch the principal," Leno tells CNBC Make It. "I've never touched a dime of my 'Tonight Show' money. Ever."

Even today, Leno, who now hosts CNBC's "Jay Leno's Garage," still does two to three comedy gigs a week, or "210 jobs a year outside of whatever else I'm doing," he says. After all, "if you do something and it works, then keep doing it."

CNBC's "Jay Leno's Garage" airs Thursdays at 10 p.m. ET.

Don't miss: How Jay Leno went from earning minimum wage at McDonald's to making millions hosting 'The Tonight Show'

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