The core "engineer mindset" is solving interesting problems. The core librarian mindset is connecting people with the information they are seeking. That's what drives them.
The last time I grabbed something rare via OhioLINK it was a twenty year old instructor's manual that accompanies a calculus textbook I own, which they shipped all the way from across the state from some little college's library. It didn't occur to me to calculate the market value of that book. But here's a test...
I see seven copies of Asimov's Annotated Paradise Lost "AVAILABLE" for borrowing and...
Your request for Asimov's annotated Paradise lost. Text by John Milton, notes by Isaac Asimov. was successful.
I fully expect this to go through but I'll make a note here if it doesn't. And hey, you should totally try this yourself, it's an interesting book. (edit: although if we're being honest that's coming from a big Asimov fan, so I'm hopelessly biased. This went out of print after one print run, so it's probably not objectively great.)
We've actually had to travel (as in physically drive to D.C.) to the Library of Congress because it was the only place that had a book.
At least in Germany, virtually all public libraries are interconnected with each other, so if one library doesn't have a particular book, another one which has it can send the book their way. And in the case that there's no library at all holding it in stock in all of Germany (which is damn near impossible), as long as the printers have fulfilled their legal obligation to send at least two copies of the book to the National Library, they'll be the "library of last resort".