4 ideas
Printing could only become a trade once rag-based paper had displaced parchment. A single Bible on vellum could consume the skins of hundreds of animals, while linen rags were abundant and cheap. Even so, paper remained the printer's largest single cost, often more than half the price of an edition, so paper supply and price shaped what could be printed and in what quantities.
Printers were businessmen who needed to recover heavy upfront costs, so they chose titles with proven demand. As a result, incunabula were overwhelmingly Latin and heavily religious: devotional works, scholastic texts and medieval romances. For decades, the press spread established ideas more widely rather than new ones. Fresh science such as Copernicus's heliocentrism circulated far less than the traditional cosmologies it challenged.
From 1517, Luther wrote short, cheap German-language tracts that printers in many towns pirated and reprinted immediately. Between 1517 and 1520, his roughly thirty publications are estimated to have sold over 300,000 copies. This made the Reformation the first mass movement carried by the printing press, which authorities could not contain.
When Church or state banned a book, production moved to presses beyond their reach, such as Geneva, the Dutch Republic or Swiss towns. Smugglers and clandestine booksellers then carried the books back across the border. Prohibition often raised a book's value and demand, turning repression into a profitable export trade for neighbouring jurisdictions.