Investing in the stocks of high-quality, growing companies for a long period of time is the most likely way for us regular folk to get rich. We're not likely to make millions being professional athletes or actors, we're probably not going to inherit millions, and we're almost certainly not going to win the lottery.

But if you're young and don't have any credit card debt or other high-cost debt, I suggest opening a brokerage account -- an IRA if you don't have one yet -- and adding as much as you can every month (up to the maximum in the case of an IRA). Consistently buying more of the right kinds of companies, through thick and thin, for a long period of time is almost certainly going to turn out very well.

And what are the right kinds of companies? We need to invest in companies with huge growth runways ahead and impenetrable competitive advantages so we can be confident that growth will continue without disruption. There aren't many companies like this, but here are three that fit the bill. Invest in these for a few decades, and you'll probably end up rich.

Amazon has loads of growth ahead

We all know Amazon (AMZN 1.49%) and what a big company it has become, but what few people realize is how much more room it has to grow over the next few decades. The global retail market is a $25 trillion market. Despite Amazon's already hefty size, its retail business, which is everything except Amazon Web Services (AWS) and Other revenue, which is mostly advertising, is only about 1% of that today.

Similarly, AWS is the global leader in the public cloud business, with a $40 billion revenue run rate, but even that is an immaterial share of what AWS CEO Andy Jassy believes is a $3.7 trillion market, only 3% of which has moved to the cloud. In addition, Amazon is constantly entering new markets, including healthcare, global logistics, grocery delivery, and physical retail stores with the Amazon GO "just walk out" technology. Considering these factors, I believe the company still has decades of growth ahead of it.

A man in a suit sitting in a chair with money raining down around him.

Image source: Getty Images.

Amazon also has enormous competitive advantages that mean it should be able to fully capitalize on its growth opportunities. For example, the company now has more than 150 million Prime members globally and is increasingly able to deliver items to them on a same-day or next-day basis for free. That is virtually impossible to disrupt.

Perhaps the best thing about Amazon is its pioneering culture. The company is constantly inventing new products and services and creating new businesses from scratch. Some of them will probably turn into big businesses in the future. That's just another reason Amazon is almost inevitably going to be far larger and more profitable in the years to come.

Netflix is only scratching the surface

Like Amazon, Netflix (NFLX -0.08%) doesn't need much of an introduction. It is the largest subscription video-on-demand (SVOD) business in the world, with 167 million global paid subscribers. It spent about $15 billion of cash on content last year and expects to spend even more this year, which is a multiple of what any other streaming service is spending on content.

Like Amazon, Netflix still has a massive global opportunity ahead of it. Globally, there are about 1.7 billion households today outside of China, where Netflix doesn't operate. At average population growth rates, that should become about 2.0 billion in 20 years. By then, the vast majority of them should have high-speed internet connections given the secular trend of increasing global connectivity. Given Netflix's content strategy and budget, it is likely to have loads of compelling content for every demographic and every interest group around the world, which should make it an attractive service for virtually everyone worldwide.

New streaming competition from Apple, Walt Disney, AT&T's HBO Max, and others is unlikely to make a dent in Netflix's success. I believe the majority of these global households will subscribe to Netflix a couple decades from now, while some will add on other niche services. That's why Netflix is a perfect stock to buy now, and buy more of every so often, if you want to end up rich.

Berkshire Hathaway delivers solid, steady growth

Berkshire Hathaway (BRK.A 0.99%) (BRK.B 0.91%) will almost certainly grow the slowest of these three companies, but its long-term future is rock solid. It is the world's largest insurance company by market cap, with a fortress balance sheet designed to withstand even the worst global catastrophes.

It has a large group of wholly owned subsidiaries, some of which would be Fortune 500 companies were they stand-alones, including Burlington Northern Santa Fe, Berkshire Hathaway Energy, Lubrizol, Marmon, and Precision Castparts. Of course, it also maintains a large portfolio of publicly traded stocks, including Apple, Wells Fargo, Bank of America, American Express, and Coca-Cola.

Berkshire Hathaway is run by arguably the world's greatest investor, Warren Buffett, and his legendary sidekick, Charlie Munger. Buffett is turning 90 in August of this year, so he won't be at the helm forever, but he appears to have created a culture at Berkshire that will survive well beyond him. Berkshire is also trading cheaply at the moment, at only about 1.2 times its book value, so the stock should perform well over time. As importantly, Berkshire should be much bigger and more profitable in the distant future, so investors can be confident enough to buy it and keep buying it.