Bernie Ebbers and Ken Lay were caricatures - they were easy to spot. They were almost psychopaths. But it's much harder to spot problems at companies like Royal Dutch [Shell].

There are two kinds of businesses: The first earns 12%, and you can take it out at the end of the year. The second earns 12%, but all the excess cash must be reinvested - there's never any cash. It reminds me of the guy who looks at all of his equipment and says, 'There's all of my profit.' We hate that kind of business.

The way to win is to work, work, work, work and hope to have a few insights And you're probably not going to be smart enough to find thousands in a lifetime. And when you get a few, you really load up. It's just that simple.

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

I find it quite useful to think of a free-market economy - or partly free market economy - as sort of the equivalent of an ecosystem. Just as animals flourish in niches, people who specialize in some narrow niche can do very well.

It's not given to human beings to have such talent that they can just know everything about everything all the time. But it is given to human beings who work hard at it - who look and sift the world for a mispriced bet - that they can occasionally find one. And the wise ones bet heavily when the world offers them that opportunity. They bet big when they have the odds. And the rest of the time they don't. It's just that simple.

A foreign correspondent, after talking to me for a while, once said: "You don't seem smart enough to be so good at what you're doing. Do you have an explanation?"