The biggest challenge in the stock market is not Mr. Market or Mr. Value. The biggest challenge is neither visible nor measurable; it is hidden in the emotional incapacities of each of us as investors. Investing, like parenting teenagers, benefits from calm, patient persistence with a long-term perspective and constancy to purpose. That's why "know thyself" is the cardinal rule in investing.

The hardest work in investing is not intellectual; it's emotional. Being rational in an irrational, short-term environment is not easy, particularly with Mr. Market always trying to trick you into making changes. The hardest work is not figuring out the optimal investment policy; it's sustaining a long-term focus—particularly at market highs or market lows—and staying committed to your optimal investment policy.

—Charles D. Ellis