I really want to plug Carl and his website BehaviorGap.com for the message they have to investors. Please visit the site and learn more about what the 'Behavior Gap' is. Here it is in a nut-shell (if you're a client of ours you will note that it is very similar to the advice you get).
Mutual fund through their portfolio managers deliver return each year whether positive or negative. The vast majority of Investors, investing in those mutual funds have very clearly received less return on their invested money than the funds performed.
Because investors on the whole tend to invest during market rallies (the peak of a cycle) and after the rally falls from its high price, investors sell. This by definition is buying high and selling low. This is worse investing strategy there there is. The difference between what investors make and what their mutual funds make is coined the Behavior Gap. At BehaviorGap.com they preach that your investment returns are determined by your behavior.