Although somewhat counterintuitive, an individual stock’s volatility in and of itself, is not the most important consideration when assessing risk. Consider a situation in which an investor could, without incurring additional cost, reduce the volatility associated with her portfolio of assets. This is most commonly accomplished through diversification. Consider holding two stocks that have the same expected returns, instead of one stock. Because stock returns will not be perfectly correlated with each other, it is unlikely that both stocks will experience extreme movements (positive or negative) simultaneously, effectively reducing volatility of the overall portfolio. As long as assets do not move in lock step with one another (are less than perfectly
positively correlated), overall volatility can be reduced, without lowering expected returns, by spreading the same amount of money across the multiple assets.