To start with, no one knows the required operational cash for a year. That is to say the Library has no budget for being run. Instead whatever the budget handed down is your bottom line. Also, monies are very specific. You can buy books, books and books and yet you cannot pay someone to catalog the books, or source purchasing the books. So a library can have millions of dollars waiting for someone to buy books and be unable to pay its utility bill.
And this is a microcosm's for the Federal way of doing things as well.