Paper

Paper as a sheet of beaten plant fiber is credited to Han China, traditionally to Cai Lun around 105 CE. He did not invent fiber sheets from nothing. He standardized a process, using bark, hemp, rags, and nets, that could be made in quantity. Earlier scraps exist.

The contribution is a writing surface cheaper than bamboo, silk, or parchment. A book stops being a luxury object made from animals. Bureaucracy, exams, and later printing all need a surface you can afford to waste.

Paper reaches the Islamic world by the 700s, Europe much later, and becomes common in Europe only after mills in the 1200s and 1300s. The printing press in Germany sits on Chinese paper plus European metallurgy and the screw press.

Without paper, people still write. They write less, and they write on things that do not scale. The press does not create the demand for copies by itself. Cheap sheets are half of that.