You need some physical, trusted party to reconcile the state of the paper with the state of the real world... Otherwise known as working State with an army, a

You need some physical, trusted party to reconcile the state of the paper with the state of the real world... Otherwise known as working State with an army, a navy, nukes, and democracy (for stability), or some semblance thereof, and all the other stuff that keeps it humming along for 200+ years despite internal turmoil, foreign attacks, and all that. And rich enough to keep its economy humming too, and its coffers flush with cash and other reserves. That's what makes a stable currency; not "fiat" or "paper stacks".