Write what you care about and understand. Writers should never try to outguess the marketplace in search of a salable idea; the simple truth is that all good books will eventually find a publisher if the writer tries hard enough, and a central secret to writing a good book is to write on that people like you will enjoy.
Richard North Patterson
Naturally, my wife and friends wanted to know how a financial writer who was knowledgeable about the markets could make that kind of mistake. I don't have a good answer. But I did learn a valuable lesson: Don't try to outguess the market. Decide on your long-term investment strategy, and as long as it's the right strategy for you, stick to it.
It can be shown that maximum diversification is achieved by holding each stock in proportion to its value to the entire market (italics added)... Hindsight plays tricks on our minds... often distorts the past and encourages us to play hunches and outguess other investors, who in turn are playing the same game. For most of us, trying to beat the market leads to disastrous results... our actions lead to much lower returns than can be achieved by just staying in the market.