Warren Buffett knows a lot about a lot.

Anyone who has read his annual letters to Berkshire Hathaway (NYSE:BRK.A) (NYSE:BRK.B) shareholders will appreciate just how much Mr. Buffett knows about investing, his businesses, life in general, and even country music. But it's what he admits that he doesn't know that might be even more interesting. Here are five things Warren Buffett doesn't know that could help all of us invest better.

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1. How to reliably predict market movements

In his 2014 letter to shareholders, Warren Buffett said, "Since I know of no way to reliably predict market movements, I recommend that you purchase Berkshire shares only if you expect to hold them for at least five years. Those who seek short-term profits should look elsewhere." That advice is applicable for investing in pretty much any stock, not just Berkshire Hathaway.

The truth is that no one can consistently predict short-term market movements. However, it doesn't take someone with Warren Buffett's expertise to accurately predict market movements over long periods of time. Over the long run, stock prices have historically gone up. Knowing that you can't predict the short term but can realistically expect gains over the long term by investing in solid businesses will make you a more successful investor.

2. Anything about farming

Buffett stated in his 2013 letter that he knew nothing about farming. It's important to understand the context of this remark. He bought a 400-acre farm in 1986 with no clue about how to run it. However, his son did know something about farming -- and helped Buffett estimate the potential risks and rewards for the investment. Like many of his investments, the farm turned out to be a good pick over time.

How does Warren Buffett's ignorance about farming help ordinary investors? Realize that you don't have to understand everything about a business for it to be a smart investment choice.

For example, I recently bought AbbVie stock. I'd be lying if I said that I fully understood all of the science behind the biotech's drugs and pipeline candidates. However, I researched the company's prospects and its challenges. I learned enough about AbbVie to think that it was a good long-term investment. Like Warren Buffett and his farm, I didn't have to know all of the details to gain an understanding of the big picture.

3. Answers to all-important questions

Hurricane Katrina, the most destructive hurricane in U.S. history, struck in 2005. Following the devastation of this storm and an apparent increase in the number of category five hurricanes, Buffett wrote that he and the heads of Berkshire's reinsurance businesses didn't know the answers to "all-important questions" about whether or not more severe storm activity would continue.

The important thing to learn is what Buffett and Berkshire did in respond to not knowing these answers. They exercised caution by increasing policy premiums and limiting aggregate exposure. However, investors should also note that Buffett didn't abandon a profitable business just because of the setbacks in 2005.

We don't know what storms will hit the stock market, either. Because of this ignorance, investors should take steps to minimize risk. Diversification across multiple stocks and multiple industries is a key way to reduce risk. But we shouldn't forfeit good opportunities because of what we don't know.

4. Of any board that is as aligned with shareholder interests

Buffett also stated in his 2005 letter that he didn't know of any "other board in the country in which the financial interests of directors are so completely aligned with those of shareholders" as much as Berkshire's board. This alignment with shareholder interests is a common theme in Buffett's letters.

Why is this relevant for investors who don't own Berkshire stock? It's a good idea to pay attention to the boards of directors of companies in which you own shares. The actions of the boards can make a big difference in the profitability of your investments.

In his 2004 letter, Buffett mentioned a case where board members of another company scuttled an acquisition attempt (not by Berkshire) that had been approved by management and would have greatly benefited shareholders. However, shareholders never even learned about the offer. Buffett couldn't say for sure why the board rejected the deal, but he noted that the members voted themselves a hefty increase in directors' fees in the same meeting in which they spurned the proposed acquisition.

Investors would be wise to invest in stocks of companies with boards that mirror some of the characteristics of Berkshire's board. Directors should own significant stakes in the company that weren't acquired as a result of being a member of the board. Any fees as a result of being a board member should be a tiny portion of the directors' annual income. 

5. What his businesses will earn next year -- or even next quarter

Wall Street waits on bated breath for every revenue and earnings projection made by company executives. In contrast, here's what Warren Buffett said in his 2002 letter to shareholders: 

Charlie [Munger] and I not only don't know today what our businesses will earn next year – we don't even know what they will earn next quarter. We are suspicious of those CEOs who regularly claim they do know the future – and we become downright incredulous if they consistently reach their declared targets. Managers that always promise to "make the numbers" will at some point be tempted to make up the numbers.

The key takeaway for investors from Buffett's comments are that estimates are just estimates. Don't base your investing decisions solely on them. 

One thing Buffett knows to definitely remember

We can learn plenty from what Warren Buffett doesn't know. There's at least one thing Mr. Buffett said in his 2016 letter to shareholders that he does know that is important for investors to remember also: "American business – and consequently a basket of stocks – is virtually certain to be worth far more in the years ahead. Innovation, productivity gains, entrepreneurial spirit and an abundance of capital will see to that."  

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.