Sometime after 685 AD, they invented spaces between words. All text - in Latin to that point, mostly - was written in scriptio continua.

All sorts of ambiguity and hilarity would ensue; to be a good writer, you needed to ensure that words didn't bleed together and form incorrect meanings in unintended combinations. If you lost your place when reading, you'd have to know generally where you were in a scroll, and restart from a place you remembered.

Kinda crazy to think how difficult it would be to cross reference things and do collaborative research with no spaces or pages.

I can see how it wculd take that long to realize it would be nice to have a way to tell people which page to look at in their exact copy of a book.

Many times obvious things are only obvious once you see them. Like roller suitcases.

The early printing press was probably focused on short few page documents (an increasing scale), and it wouldn't be surprising if page numbers were a solution to help printers not mix up pages.