The recent research on investment offers a number of valuable insights into how managers can evaluate opportunities, and it highlights a basic weakness of the NPV rule. When a company exercises its option by making an irreversible investment, it effectively “kills” the option. In other words, by deciding to go ahead with an expenditure, the company gives up the possibility of waiting for new information that might affect the desirability or timing of the investment; it cannot disinvest should market conditions change adversely. The lost option value is an opportunity cost that must be included as part of the cost of the investment. Thus the simple NPV rule needs to be modified: Instead of just being positive, the present value of the expected stream of cash from a project must exceed the cost of the project by an amount equal to the value of keeping the investment option alive