Coronavirus-induced lockdowns provided some with more time on their hands to try trading apps, like Robinhood, which are seeing a surge in business; millions of Americans are unemployed and may think it is a way to make up for lost income; and a lack of sports-betting or access to casinos have driven gamblers to explore the day trading trend, to name a few reasons.
"Day trading is not investing. Day trading is gambling. Nothing wrong with it. Nothing wrong with Las Vegas either. But it's not investing," O'Leary tells CNBC Make It.
And Barbara Roper, director of investor protection at the Consumer Federation of America, recently told CNBC about day trading that "losses are particularly likely in an economy that is as rife with unprecedented and unpredictable risks of the kind we face in a global pandemic that has decimated certain industries."
The difference between day trading and investing, according to O'Leary, is that investing is "putting money into the market with a long view," as in, "your entire life."
"Money is made in investments by investing and by owning good companies for long periods of time," Buffett told CNBC in March 2016. "If they buy good companies, buy them over time, they're going to do fine 10, 20, 30 years from now."
And "that's how you do it," O'Leary said. "Whether you like Warren Buffett or you don't, he understands that in the long-run, it's about the cash flow and about investing... taking positions and holding onto them for long periods of time."
"Markets have a casino characteristic that has a lot of appeal," Buffett said during the 2017 Berkshire Hathaway shareholders meeting. "People like action and they like to gamble. If they think there's easy money to be made, you get a rush. For a while, it will be self-fulfilling and create new converts, until the day of reckoning comes."
All in all, "I have no problem with day trading," O'Leary said, "but to me, you can go to Las Vegas or you can day trade. Same thing. That's not investing. That's gambling."
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Disclosure: CNBC owns the exclusive off-network cable rights to "Shark Tank."