Why does the short-run marginal-cost curve eventually increase for he typical firm?

The short-run marginal-cost curve eventually increases for a typical firm due to the law of diminishing returns. As production expands, each additional unit of output requires more variable inputs, which leads to increased costs per unit. Initially, firms may benefit from economies of scale, but after a certain point, the inefficiencies of adding more labor or materials without a corresponding increase in productivity cause marginal costs to rise. This results in an upward-sloping marginal-cost curve in the short run.