Why was the size of handmade paper limited by the papermaker’s frame and mold?

In the traditional craft of papermaking, the size of a single sheet was physically constrained by the dimensions of the frame and mold that a papermaker could manually lift from a vat of stock. Because the process required the operator to dip the mold into the vat and then lift it to allow the water to drain, the weight and surface area of the equipment were limited by human strength and handling capacity.1

This manual limitation persisted until the invention of the paper machine, which replaced the individual frame and mold with a continuous, moving screen belt, allowing for the production of unbroken sheets of paper.1