Warren Buffett is arguably the most successful investor ever. With a net worth in the neighborhood of $65 billion, the Oracle of Omaha has built one of the largest fortunes in the world, thanks to his investing skills. For this reason, legions of investors are always trying to learn from Buffett, and replicate his strategies in order to maximize their returns.

Rivers of ink have been written about Warren Buffett's philosophy. However, if I had to sum up the core of his approach in a simple and straightforward phrase, it would be this: Invest in companies with big competitive strengths for the long term.

It's all about competitive strength
Warren Buffett only invests in companies with rock-solid competitive strengths, or business moats, as he likes to call them. Competitive advantages are the factors that protect the company from the competition, allowing it to sustain superior profitability over the years.

In Buffett's own words:

The key to investing is not assessing how much an industry is going to affect society, or how much it will grow, but rather determining the competitive advantage of any given company and, above all, the durability of that advantage. The products or services that have wide, sustainable moats around them are the ones that deliver rewards to investors.

Coca-Cola (KO -0.73%) is a textbook example of a company with almost indestructible competitive strengths, and also one of the biggest positions in Berkshire Hathaway's (BRK.A -0.75%) (BRK.B -0.76%) portfolio. Warren Buffett first bough Coca-Cola stock in 1986, and Berkshire Hathaway currently owns 400,000 shares of the company, for a market value of more than $16 billion.

A big part of Coca-Cola's moat is based on brand power. Brand Coca-Cola is the undisputed global leader in carbonated drinks, and the company owns an amazing portfolio featuring 20 different brands making more than $1 billion each in global sales. This includes iconic soft-drink names such as Coke, Diet Coke, Fanta, and Sprite, and also healthier alternatives in water, juice, and tea, for example Dasani, Fuze Tea, Powerade and Minute Maid, among several others.

In addition, the company owns a gargantuan distribution network, which sets it apart from the competition, and it also enjoys abundant financial firepower to invest in areas such as marketing and R&D. Coca-Cola will need to adapt to changing customer demand in the coming years, because many consumers are moving away from soda toward healthier drinks; but the good news for investors in Coca-Cola is that the company has the resources to do so.

The power of long-term investing
Warren Buffet has said time and again that you need to have a long-term horizon to achieve superior returns from your investments. Buffett's investment in IBM (IBM -0.17%) is materially underperforming the market: IBM stock is down by 11% since January 2012, while the S&P 500 is up 62% in the same period. But Buffett is not losing his conviction in IBM; in fact, he bought even more IBM stock in the first quarter of 2015.

IBM has been delivering disappointing revenue growth lately. The company is selling its operations in hardware-related businesses to better focus on more promising opportunities in software and services. Also, new industry trends, such as cloud computing and the rise of software-as-a-service, are forcing IBM to adapt to new business models.

On the other hand, management is heavily betting on a series of businesses it has identified as "strategic imperatives" -- cloud, analytics, mobile, social, and security. These are areas with attractive growth prospects and superior profitability levels. IBM is deeply entrenched in the corporate world, and the company believes it can leverage its business know-how and industry-specific insights to outperform the competition in these businesses.

Revenue growth from the strategic-imperatives group of businesses has been in the neighborhood of 20% on a currency-adjusted basis in each of the past five years, and performance even accelerated in the first quarter of 2015, with constant-currency sales from these segments growing 30% versus the same quarter in 2014.

IBM brought in nearly $25 billion in revenue from its strategic imperative businesses in 2014, and management intends to produce $40 billion -- or about 40% of the company's total revenue -- from them by 2018. This is clearly an ambitious target, but it doesn't sound unreasonable considering recent performance and growth opportunities in these divisions.

Warren Buffett invests for the long term. He wrote in his 1988 letter to Berkshire Hathaway investors: "When we own portions of outstanding businesses with outstanding managements, our favorite holding period is forever."

From this perspective, it makes a lot of sense to see Buffett holding on to his IBM stock, and even increasing positions at attractive prices, while he waits for growth rates to accelerate once again.