Not only is STORE Capital (NYSE: STOR) in Berkshire Hathaway's (NYSE: BRK.A)(NYSE: BRK.B) stock portfolio, but it's the only real estate investment trust (REIT) the Warren Buffett-led conglomerate has chosen to put its own capital into. STORE Capital significantly underperformed the S&P 500 in 2021, with a total return of about 6% for the year versus 29% for the S&P 500 with just a few days left in the year. In a nutshell, STORE rebounded sharply from its COVID-19-fueled decline in late 2020, so much of the upside related to vaccines and the gradual easing of pandemic-era restrictions was already priced in at the start of the year. However, despite the recent underperformance, I think STORE Capital is still a great stock to add to any portfolio, for five key reasons. Image source: Getty Images. 1. Massive market opportunity STORE Capital owns nearly 2,800 properties and has a market cap of about $9.5 billion. While these may sound like large numbers (and they are), the company has tremendous growth potential ahead of it. In fact, management estimates the addressable market for net lease properties in its investable universe to be about 2 million properties worth about $3.9 trillion. Now, STORE won't ever get all of it, but if it can even scale to 1% of its addressable opportunity, it would be more than seven times its current size. 2. Excellent growth economics STORE Capital is being rather aggressive with its growth strategy. Given its size, investing $1 billion to acquire properties during the first nine months of 2021 is a pretty fast growth rate. However, when you consider the economics STORE Capital is getting, it makes sense. The average initial cap rate (operating income as a percentage of cost) on STORE's 2021 acquisitions has been 7.7%. Meanwhile, the average interest rate STORE Capital pays on debt issued in 2021 is just 2.8%. That's an extremely attractive spread. 3. Great valuation Based on the midpoint of STORE Capital's 2021 funds from operations (FFO) guidance, the stock trades for about 17 times what is essentially the real estate version of "earnings." Meanwhile, the average S&P 500 stock trades for a price-to-earnings multiple of about 30. Not only is STORE Capital growing fast, but it's cheap. 4. A growing income stream Like most REITs, STORE Capital is designed to be a total return investment. So far, we've talked about growth, but the company also pays a generous dividend. At the current share price, STORE Capital yields a little over 4.4% annually and has increased its dividend every year since its November 2014 IPO. So, in addition to its stock price likely rising over time, STORE generates a large, growing income stream for its investors. 5. Massive total return potential I mentioned that STORE Capital went public in 2014 and has generated an impressive 13.7% annualized total return for investors since then, but it doesn't exactly have a long track record to analyze. However, there are large REITs with similar business models that have been around for decades, and the total returns have been exceptional. Realty Income (NYSE: O) and National Retail Properties (NYSE: NNN) are two with comparable models that have generated total returns of 2,560% and 1,450%, respectively, over the past 25 years. Compare this with the S&P 500's 909% total return during the same period. Invest for the long term REITs are designed to be long-term investments, and STORE Capital is no exception. While I'm confident that STORE Capital has a great chance of being a great market-beating dividend stock to own for the long term, I have absolutely no idea what it will do in the coming weeks, months, or even over the next year or two. But if you measure your investment returns in longer intervals (say, five years or more), STORE Capital could be an excellent addition to your portfolio. 10 stocks we like better than STORE CapitalWhen our award-winning analyst team has a stock tip, it can pay to listen. After all, the newsletter they have run for over a decade, Motley Fool Stock Advisor, has tripled the market.* They just revealed what they believe are the ten best stocks for investors to buy right now... and STORE Capital wasn't one of them! That's right -- they think these 10 stocks are even better buys. See the 10 stocks *Stock Advisor returns as of December 16, 2021 Matthew Frankel, CFP® owns Berkshire Hathaway (B shares), Realty Income, and STORE Capital. The Motley Fool owns and recommends Berkshire Hathaway (B shares). The Motley Fool recommends STORE Capital and recommends the following options: long January 2023 $200 calls on Berkshire Hathaway (B shares), short January 2023 $200 puts on Berkshire Hathaway (B shares), and short January 2023 $265 calls on Berkshire Hathaway (B shares). The Motley Fool has a disclosure policy.Source