The Long-Run Zero-Profit EquilibriumIf existing firms are profitable, entry will occur and shift each existing firm’s demand curve leftward. If existing firms are unprofitable, each remaining firm’s demand curve shifts rightward as some firms exit the industry. Entry and exit will cease when every existing firm makes zero profit at its profit-maximizing quantity. So, in long-run zero-profit equilibrium, the demand curve of each firm is tangent to its average total cost curve at its profit-maximizing quantity: at the profit-maximizing quantity, QMC, price, PMC, equals average total cost, ATCMC. A monopolistically competitive firm is like a monopolist without monopoly profits.