I was wrong about linen thread until I saw those medieval manuscripts.
Always used polyester thread for my bindings. Thought it was stronger and easier. Went to a museum in Edinburgh last fall. They had prayer books from the 1200s on display. The linen thread stitching was still perfect after all that time. Changed my mind completely. Now I only use linen for my personal projects.
Seriously, I used to think linen was just a fancy word for scratchy fabric. But @the_robin's library story and my own grandma's quilts changed my mind. Seeing her old linen curtains last 50 years while my "easy-care" ones fell apart after five was a real wake up call. It's crazy how something so simple can just hold up forever. What's the oldest linen item you've got hanging around?
You know my friend Kevin who works in a library archives? He had the same thing happen with some 1800s ledgers. The linen stitching was the only thing not falling apart. Made him switch over for his own stuff too.