The Monopolistically Competitive Firm in the Short RunThe firm in panel (a) can be profitable for some output quantities: the quantities for which its average total cost curve, ATC, lies below its demand curve, DP. The profit-maximizing output quantity is QP, the output at which marginal revenue, MRP, is equal to marginal cost, MC. The firm charges price PP and earns a profit, represented by the area of the green shaded rectangle. The firm in panel (b), however, can never be profitable because its average total cost curve lies above its demand curve, DU, for every output quantity. The best that it can do if it produces at all is to produce quantity QU and charge price PU. This generates a loss, indicated by the area of the orange shaded rectangle. Any other output quantity results in a greater loss.