Matt Higgins went from cleaning tables at a fast-food restaurant to becoming a self-made millionaire and guest investor on ABC's "Shark Tank."

Higgins, the CEO of private investment firm RSE Ventures, credits that journey to a simple three-word question, he told graduating students at Rockville Centre, New York-based Molloy University on Monday.

"Life is not dictated by where we begin, or even where we end up, but how much distance we cover in between," said Higgins. "And the way to cover more distance than you ever dreamed possible is to repeatedly ask yourself one simple question ... Why not me?"

He recommended the question as an antidote to imposter syndrome, something about 70% of people experience during their lifetime.

"When you take those first tentative steps in the direction of your new life, you will feel like an imposter," Higgins said. "I certainly did when I became a guest Shark on 'Shark Tank.' A guy from Queens with a GED competing against Mark Cuban and Mr. Wonderful? Come on."

Asking yourself "why not me?" can help encourage your brain to chase opportunities you might otherwise not even consider, Higgins said. In his case, the mindset helped him earn the role of youngest mayoral press secretary in New York history at age 26, going from making $35,000 to $100,000 per year.

In 2012, he co-founded RSE Ventures, the company that helped make him a millionaire.

"Shark Tank" co-star Barbara Corcoran benefited from a similar mindset, she's said. At age 23, when she started her real estate firm, The Corcoran Group, she didn't think she was worthy of wealth.

"I didn't know a rich person," Corcoran said in a live Q&A on her Patreon platform earlier this year. "My family was lower-middle class. So for me to really talk about my aspirations and feel OK dreaming them was difficult."

Corcoran said she'd tell herself, "I have the right to be rich. I have the right to desire the most for myself. I have the right to create something out of nothing, to employ people, to go on expensive vacations."

"I didn't [believe it] until I was in business maybe a dozen years. But I wish I had been a little bit easier on myself," she said.

You'll inevitably be faced with situations that make you second-guess your capabilities, but stepping out of your comfort zone with an ambitious attitude can help you keep moving forward, said Higgins.

"Never let anyone convince you that your past puts a ceiling on your future; it only sets the floor," he said. "And for all the blessings you pursue and all the burdens you must carry, always ask yourself the one question that has the power to change your life: Why not me?"

Disclosure: CNBC owns the exclusive off-network cable rights to "Shark Tank," which features Barbara Corcoran as a panelist and Matt Higgins as a guest panelist.

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