What is the meaning of Modern portfolio theory?

This approach to making investment decisions focuses on potential return in relation to potential risk. The strategy is to evaluate and select individual securities as part of an overall portfolio rather than strictly for their own investment qualities. Asset allocation is a primary tactic, according to theory practitioners, because it allows investors to create portfolios to get the strongest possible return without assuming a greater level of risk than they are comfortable with. Another tenet of portfolio theory is that investors must be rewarded (in terms of a greater return) for assuming greater risk. Otherwise, there would be little motivation to make investments that might result in a loss of principal.