The most important thing in terms of your circle of competence is not how large the area of it is, but how well you've defined the perimeter.

If you know how to value businesses, it's crazy to own 50 stocks or 40 stocks or 30 stocks, probably because there aren't that many wonderful businesses understandable to a single human being in all likelihood. To forego buying more of some super-wonderful business and instead put your money into #30 or #35 on your list of attractiveness just strikes Charlie and me as madness.

It's far better to buy a wonderful company at a fair price than a fair company at a wonderful price.

The best way in my view is to just buy a low-cost index fund and keep buying it regularly over time, because you'll be buying into a wonderful industry, which in effect is all of American industry... People ought to sit back and relax and keep accumulating over time.

John Maynard Keynes essentially said, don't try and figure out what the market is doing. Figure out a business you understand, and concentrate.

If the world couldn't see your results, would you rather be thought of as the world's greatest investor but in reality have the world's worst record? Or be thought of as the world's worst investor when you were actually the best?

If you are not willing to own a stock for 10 years, do not even think about owning it for 10 minutes.