The Modigliani-Miller Proposition II (MM2) is a cornerstone in the field of corporate finance, positing that in a frictionless environment with perfect capital markets, the cost of equity capital is linearly related to a firm’s leverage. This paper critically re-evaluates this proposition, particularly examining the determination of the cost and value of equity. We find that under specific circumstances, especially when the value of a tax shield is influenced by endogenous variables, the cost and value of equity may be ambiguous. This calls into question the universal applicability of MM2. Our research offers new perspectives on the theoretical underpinnings of financial management and underscores the significance of situational factors in the practical application of these theories.