Final answer:
Movable print must be set in reverse for printing so that the final print reads correctly from left to right, like the reversed design of a sealed mold ensures the correct appearance when stamped.
Step-by-step explanation:
The reason movable print must be laid out backward is due to the nature of the printing process. When creating a mold for printing, the text needs to be set in reverse so that the final print appears correctly when it is pressed onto paper. This mirrors how a seal works, where the design is reversed in the mold to ensure it appears correctly once stamped. The analogy of an unusual and rare mirror referenced in the question highlights an error where a mold made for casting a mirror did not account for this reversal, resulting in backward characters. Similarly, in typesetting, each letter must be reversed so that when it's transferred onto the page, it reads correctly from left to right. Another related concept is the layout of books, which follows the two-side rule where new chapters or parts start on the right-side pages, sometimes leaving blank reverse pages, much like the traditional function of a 'back' button in a web browser provides a path to the previous step or page.