The richest man in the world, Bill Gates, has been friends with Warren Buffett for over 20 years. Bill Gates has learned a lot from Warren Buffet over that time and recently revealed three insights he's picked up from him over the years.

1. There's more to investing than numbers

Before Bill Gates met Buffett he was not that interested in what Buffett did. Gates said that he figured that Buffett "just used various market-related things — like volume, or how the price had changed over time — to make his decisions." Gates didn't realize Buffett has a whole framework for how he thinks about business and investing.

When they met in 1991, Buffett peppered Gates with questions about Microsoft's (NASDAQ:MSFT) competitive advantages and why IBM (NYSE:IBM) couldn't do what Microsoft did. Gates learned that Buffett treats stocks as though he owns the entire business and not just a piece of paper. Gates also learned that Buffett is primarily concerned with investing in businesses with sustainable competitive advantages, what he calls moats, and businesses that he can understand. Warren continually works to expand this knowledge, what he calls his circle of competence, and believes that knowing the boundaries of your circle of competence is one of the most important skills an investor can have.

It is remarkable that when they met in 1991, Buffett still did not own a computer.

Buffet's old fashioned ways and his famous quote that he doesn't invest in technology companies because he doesn't understand them are frequently misinterpreted.

While Buffett understood what Microsoft did, he could not reasonably predict how the competitive forces would play out over the long term and how Microsoft would fare. As Buffett explained in some speeches in 1999 that were collected by Carol Loomis in Fortune: "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."

While Buffet didn't understand the competitive dynamics of the technology industry then, he kept learning. In the years since, Buffet has added one major technology company to his portfolio. IBM is now one of Buffett's four top holdings.

2. Be transparent and speak your mind

The second insight Gates picked up from Buffett is that you need to speak up for what you believe in. Gates notes that Buffett's letters to shareholders and interviews are so popular because you can learn a lot from them. They are also popular because Buffett is "not afraid to take positions, like his stand on raising taxes on the rich, that run counter to his self-interest." For shareholders and employees, this means keeping up with your investments whether they are the company you work for or stocks you own, and taking stands when the companies are doing something you don't agree with. Activist investors and regular shareholders frequently get proposals put on companies' proxy statements so shareholders can vote on them. Read through the proposals and vote; your votes actually matter. As Fool contributor Selena Maranjian wrote, "When I own shares of controversial companies, I can vote to change their behavior." So far in 2014, according to Broadridge Financial 123 companies had their executive pay-plans not get approved by shareholders. Besides say-on-pay votes, there are a whole host of issues that come up. Just a few from this year:

Cracker Barrel shareholders voted down a proposal to put an activist shareholder on its board and against a special dividend.

shareholders voted down a proposal to put an activist shareholder on its board and against a special dividend. Cliffs Natural Resources shareholders voted on its board of directors, voting in a slate from activist investor Casablanca, and voting out the incumbents.

Some investors take this further and only invest in companies they believe are doing good for all stakeholders. Motley Fool analyst Alyce Lomax's investing process integrates socially responsible investing factors into stock analysis which you can read about more here.

3. Time is a more precious resource than money

As Gates puts it, "No matter how much money you have, you can't buy more time. There are only 24 hours in everyone's day. Warren has a keen sense of this." Despite numerous people wanting to meet with him Buffett spends most of his days by himself deeply focused on what matters for him and his investments. He doesn't let himself get distracted by meetings or other things that take up time but provide little value. For investors, Buffett's idea of a circle of competence is also relevant here. Buffett doesn't waste time trying to find investments in businesses or technologies that he is not able to understand. While Warren is constantly learning, he only invests in businesses where he can understand how the company's competitive advantage will protect it from competitors over time. Otherwise, Warren puts the idea in his "too hard"pile and moves on to the next one.

As Buffet has said, "The difference between successful people and really successful people is that really successful people say no to almost everything." As an investor, Buffett spends most of his time reading annual reports, trade publications, and learning every day. This intensive focus was always a hallmark of Bill Gates at Microsoft, and continues to be his hallmark now at the Gates Foundation.

Charlie Munger has said that the secret of Buffett's success is that Buffett always keeps learning and improving. Bill Gates obviously continues to learn and improve just as well.