Those who have already owned shares of Chipotle Mexican Grill (CMG 0.98%) for years are familiar with the stock's potential -- it's generated stellar investment returns and life-changing wealth. A $10,000 investment at the time of its 2006 IPO would be worth over $660,000 today.

Sometimes the best business models are the simplest, and it doesn't get more straightforward than meat, beans, and rice. How has Chipotle turned such simple food into an empire? Here is the company's secret to success, and why the stock can help you retire a millionaire.

Chipotle packs flavor and variety in every bite

For those unfamiliar with Chipotle, it's a Mexican food casual dining chain that operates primarily in the United States. Today there are 3,437 restaurants, all company-operated. Customers can enjoy a small, focused menu of select proteins and vegetables served as burritos, bowls, or salads.

The genius of Chipotle's menu is its simplicity, yet it offers so many customization options. Customers specify every aspect of the product, which comes with simple choices like white or brown rice and mild, medium, or hot salsa. The simplicity means Chipotle can control inventory and use fresh ingredients, bolstering product quality and customer experience.

Like other successful restaurant models, Chipotle has spent years building brand power and locking customer loyalty with a rewards program. Chipotle's size and control over its stores give it the benefits of size and scale, which makes replicating the model and food quality difficult at Chipotle's price points.

Big profits drive expansion

Chipotle's financial flywheel is also simple. The more stores Chipotle opens, the more it can drive down costs with its size. The more profits Chipotle makes, the more stores it can open. It's a beautiful chicken-and-egg example that has helped the company steadily expand for over two decades. Chipotle is a juggernaut today with nearly $10 billion in annual sales.

The first Chipotle opened in the early 1990s, and it took nearly 20 years to open its thousandth store. But the store count has more than tripled in the 14 years since then.

And there's more. Chipotle doesn't need to invest every dollar in the business as profits build up. So it's repurchased shares over the years, slowly shrinking its share count, which means more profits per share of company stock:

CMG Free Cash Flow Per Share Chart

CMG Free Cash Flow Per Share data by YCharts

This is the secret recipe and the primary reason Chipotle stock has been a winning investment.

Will the recipe keep working?

Chipotle's recipe is why the stock could help you retire a millionaire (as part of a diversified portfolio). Simply put, 3,300 restaurants aren't that many in the grand scheme. Here are the U.S. store counts for some popular restaurant chains:

  • Taco Bell: 7,936
  • KFC: 4,290
  • McDonald's: 13,528
  • Starbucks: 16,482

As you can see, Chipotle is a fraction of the size of most direct and indirect competitors. Additionally, I like Chipotle's international potential due to the freshness of its food and the cultural diversity that its food represents. Chipotle has a handful of locations in Canada, the United Kingdom, France, and Germany, and is opening up in the Middle East.

A global footprint of 10,000 stores doesn't seem out of reach, meaning investors have years of growth ahead. Plus, how many shares will management gobble up over the next decade? Could Chipotle see a quarter of its shares retired? There's no way of knowing for sure, but it seems that Chipotle's recipe for success is something it can continue replicating for the foreseeable future.

It doesn't have to be complicated to be effective. Chipotle is a stock long-term investors can buy, tuck away, and glance at a couple of times every year to make sure the train is still on the tracks.