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.

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.

A decade ago, I really did believe that the average investor could do it himself. I was wrong. I've come to the sad conclusion that only a tiny minority, at most one percent, are capable of pulling it off. Heck, if Helen Young Hayes, Robert Sanborn, Julian Robertson, and the nation's largest pension funds can't get it right, what chance does John Q. Investor have?

Mutual fund manager performance does not persist and the return of stock picking is zero.

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

Bluntly put, there's no chance that your doctor, dentist, or attorney is a high-school dropout. Your stockbroker, however, just might be.

The essence of effective portfolio construction is the use of a large number of poorly correlated assets.