Assuming that the firm has an optimal debt/equity ratio, most textbooks recommend using the weighted average cost of capital as a cutoff rate for investment decision-making. Arditti [1] demonstrates that the components of the weighted after-tax cost of capital, as recommended by most textbooks, have been incorrectly specified. This misspecification implies that the capital structure that minimizes the weighted average after-tax cost of capital is a non-optimal one. In this paper we extend Arditti's argument and demonstrate that the finance textbooks' traditional post-tax cash flow can be misleading. Basically, there are two mistakes in these texts: one in defining the project's cash flow and one in defining the cost of capital. While these two mistakes may offset each other in some cases, therefore presenting the firm with the correct accept-reject decision, generally the two mistakes do not cancel, and the textbook procedure leads the firm to an incorrect decision. The traditional weighted average post-tax cost of capital presented in leading textbooks (cf. [4], [1I], and [12]) and taught in most courses, including those taught by the authors of this paper we denote as ct, defined as