The idea of excessive diversification is madness. Wide diversification, which necessarily includes investment in mediocre businesses, only guarantees ordinary results.

Some years ago one oil company bought a fertilizer company, and every other major oil company practically ran out and bought a fertilizer company. And there was no more damned reason for all these oil companies to buy fertilizer companies, but they didn't know exactly what to do, and if Exxon was doing it, it was good enough for Mobil and vice versa.

The possibility that stock value in aggregate can become irrationally high is contrary to the hard-form "efficient market" theory that many of you once learned as gospel from your mistaken professors of yore. Your mistaken professors were too much influenced by "rational man" models of human behavior from economics and too little by "foolish man" models from psychology and real-world experience.

If you, like me, lived through 1973-74 or even the early 1990s... There was a waiting list to get OUT of the country club - that's when you know things are tough. If you live long enough, you'll see it.

Darwin paid particular attention to disconfirming evidence. Objectivity maintenance routines are totally required in life if you're going to be a great thinker.

Over the very long term, history shows that the chances of any business surviving in a manner agreeable to a company's owners are slim at best.

We like our current shareholders and don't want to entice anyone to become one. It would help current shareholders to hear our CEOs [of the Berkshireoperating subsidiaries], but we promised them they could spend 100% of their time on their business. We place no impediments on them running their businesses. Many have expressed to me how happy they are that they don't have to spend 25% of time on activities they didn't like.