It's bad enough that you have to take market risk. Only a fool takes on the additional risk of doing yet more damage by failing to diversify properly with his or her nest egg. Avoid the problem-buy a well-run index fund and own the whole market.

No one in his right mind would walk into the cockpit of an airplane and try to fly it, or into an operating theater and open a belly. And yet they think nothing of managing their retirement assets. I've done all three, and I'm here to tell you that managing money is, in its most critical elements even more demanding than the first two.

You have to understand your own psychology. You have to understand that human beings weren't really designed to invest. We have all these emotions that are appropriate responses if you're being chased by a tiger, but they're terrible responses if you've got a 30-year time horizon to think about investment or when you're trying to manage investment over 30 years.

There are two kinds of investors, be they large or small: those who don't know where the market is headed and those who don't know what they don't know. Then again, there is a third type of investor: the investment professional, who indeed knows he doesn't know, but whose livelihood depends upon appearing to know.

Investment success accrues not so much to the brilliant as to the disciplined.

It's human nature to find patterns where there are none and to find skill where luck is a more likely explanation (particularly if you're the lucky manager).

You have to understand what market history looks like. What market history tells you is that the very, very best investments are made when things look the worst.