The top cryptocurrencies by market value, including bitcoin and ether, are plunging on Tuesday amid a sell-off. Among those is meme-inspired cryptocurrency dogecoin, which is down about 77% since its all-time high of nearly 74 cents in May.

But investor Glauber Contessoto, whose dogecoin holdings previously surpassed a value of $1 million, isn't worried.

"You just gotta zoom out and chill," Contessoto, 33, told CNBC Make It. Though he isn't a financial expert, he's optimistic that dogecoin has already hit bottom. The coin hit 16 cents Tuesday morning before inching up to 17 cents.

Between his savings and borrowed funds, Contessoto said, he invested over $250,000 in dogecoin on Feb. 5 when it was priced at about 4.5 cents. About two months later, on April 15, he said, he became a dogecoin millionaire on paper.

Since then, Contessoto has refused to sell, despite dogecoin's ups and downs. Even in May, when the value of his holdings surpassed $2 million, he still didn't budge. Now, with dogecoin trading around 17 cents, he continues to buy the dip.

"I can't pass up a good bargain," Contessoto said. Last week, he bought over $5,300 worth of dogecoin when it was around 17 cents, he said.

"Doge is my savings account," he said.

As of around 2:50 p.m. EST on Tuesday, his dogecoin holdings were worth $700,217.09.

However, financial experts are highly skeptical of dogecoin, as well as other cryptocurrencies. Their extreme volatility is one reason experts say that crypto is a risky, speculative investment.

Some warn investors to be especially cautious when investing in dogecoin in particular, since it lacks the scarcity and technological development that bitcoin has, for example. Investors could get burned, so they should invest only what they can afford to lose.

"You risk losing nearly all the money you put in," James Ledbetter, editor of fintech newsletter FIN and CNBC contributor, previously told CNBC Make It. "It has no intrinsic value and it could just as easily come crashing down in price as continue to go up."

Contessoto himself also tells his followers not to invest more than they could afford to lose.

Nonetheless, Contessoto's plan remains the same: "Once I hit $10 million, then I'll take out 10%."

"I had a game plan in mind going into this purchase, and I wouldn't feel right always telling people to 'buy and hold' and as soon as I hit $3 million, cash out and leaving everyone else hanging," he said. "Until I reach my goal, I'll continue to buy, hold and 'diamond hand' it."

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