Today, investors are caught at an intellectual crossroad. To the left lies the pathway of modern portfolio theory. It assumes that investors are rational, the market is efficient, risk is defined by price volatility, and the only way to reduce risk is to diversify broadly. To the right lies the focus portfolio theory. It is distinctly separate and is grounded in this very different set of beliefs:
Investors are not always rational; they suffer from periodic episodes of fear and greed.
The market is not always efficient, and therefore investors willing to study and learn are given opportunities to beat the market.
Risk is not price-based; it is economic-value-based.
The optimal portfolio is a focus portfolio that stresses big bets on high-probability events, as opposed to equally weighted bets on a mixed bag of probabilities.