The hedge fund known as "Long Term Capital Management" collapsed last fall through overconfidence in its highly leveraged methods, despite I.Q.'s of its principals that must have averaged 160. Smart people aren't exempt from professional disasters from overconfidence. Often, they just run aground in the more difficult voyages they choose, relying on their self-appraisals that they have superior talents and methods.

Financial institutions make us nervous when they're trying to do well.

Rationality is not just something you do so that you can make more money, it is a binding principle. Rationality is a really good idea. You must avoid the nonsense that is conventional in one's own time. It requires developing systems of thought that improve your batting average over time.

Knowing what you don't know is more useful than being brilliant.

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 normal expectancy of the average investor - for example, the pension funds of AT&T or IBM - is 6% for a long time.

Once you start doing something bad, then it's easy to take the next step - and in the end, you're a moral sewer.