Want to know two amounts that just might blow you away? Here they are -- $2.07 and $675.67. To be blown away, though, you need to understand the context.

If you had invested only $2.07 one year ago in Shiba Inu (SHIB 1.39%) and held on to your coins, you'd now have $1 million based on the trading price at the time of this writing. To have that cool million with Ethereum (ETH 1.36%), you would have needed to buy $675.67 of the coins in July 2015. 

Making a fortune with such small upfront investments in such a short period of time certainly blows me away. But could Ethereum and Shiba Inu still be millionaire-makers?

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The keys to their success so far

To evaluate the future prospects of Shiba Inu and Ethereum, it's important to first understand why the digital tokens have achieved such tremendous success in the past. The biggest reason for their fantastic gains has been the rapid rise in the popularity of cryptocurrencies, in general. 

Investing in cryptocurrency has moved from the fringes to the mainstream over the last few years. This trend has brought more people into the market, driving demand (and coin prices) significantly higher.

These two cryptocurrencies also have unique factors behind their success. Shiba Inu, for example, piggybacked off of the huge popularity of Dogecoin (DOGE 0.31%). Both tokens use the Shiba Inu Japanese hunting dog as their mascots. Elon Musk's tweets of photos of his Shiba Inu puppy helped attract attention for the cryptocurrency Shiba Inu.

Ethereum's impressive rise stemmed in large part from the strength of its technology. The Ethereum blockchain supports smart contracts that enable anonymity of both parties to a transaction with no intermediary required.

It didn't take long for Ethereum to become the top blockchain platform. Thousands of decentralized apps now run on top of Ethereum -- notably including Shiba Inu itself. 

Current situations

The situations for Shiba Inu and Ethereum are quite different now compared to when the cryptocurrencies were first launched. They're both household names (at least, in many households). 

Shiba Inu's market cap currently stands at close to $21 billion, enough to make it the No. 12 biggest cryptocurrency in the world. Ethereum ranks as the second-largest cryptocurrency with a market cap of around $500 billion. Neither digital token can enjoy the novelty of being the shiny new crypto any longer.

Of course, Shiba Inu doesn't have to ride on the coattails of Dogecoin now. On the other hand, Musk's tweets are less likely to boost the cryptocurrency, especially after the billionaire revealed that he doesn't own Shiba Inu.

Probably the biggest challenge for these digital tokens going forward is that they have a lot of competition. There are thousands of cryptocurrencies vying to knock Shiba Inu off its perch. Ethereum faces newer blockchains that are much faster and cheaper.

Still millionaire-makers?

With all of that being said, let's return to our key question about whether or not these two cryptocurrencies could still be millionaire-makers. The correct answer is "yes." Nearly any asset holds the potential to make $1 million with a large enough initial investment and a long enough holding period.

But could you buy $2.07 of Shiba Inu and $675.67 of Ethereum tokens today and become a millionaire over the next decade? It's highly unlikely (and I'm being generous with that phrasing).

The past successes of both cryptocurrencies make it practically impossible to repeat their staggering gains. For example, Shiba Inu's market cap would have to skyrocket to more than $10.1 trillion. At that level, the cryptocurrency would be worth roughly as much as all of the FAANG stocks plus Microsoft combined. Etheruem would need to grow to more than 30 times the current U.S. gross domestic product.

Putting aside the $1 million threshold, though, could Shiba Inu and Ethereum still make a lot of money for investors who buy today? Sure. However, there are still plenty of risks. I'd say there are more risks for Shiba Inu than Ethereum because of the latter's widespread adoption. 

I think that there are other cryptocurrencies that will likely be bigger winners than Shiba Inu or Ethereum over the next few years. And maybe, just maybe, some of them could even become millionaire-makers.