Labor’s negative marginal product for L > 5 may arise from congestion in the chair manufacturer’s factory. Since more laborers are using the same fixed amount of capital, it is possible that they could get in each other’s way, decreasing efficiency and the amount of output. Firms also have to control the quality of their output, and the high congestion of labor may produce products that are not of a high enough quality to be offered for sale, which can contribute to a negative marginal product.