The Finnish experiment failing because people just deposited their cash in banks first is a classic example of Goodhart's Law in action. Or as I like to call it, "If you tell people you're going to cut their money in half, they'll find a way to keep it whole."
What's really interesting is Belgium's more successful approach, they went full scorched earth on 2/3 of their money supply and somehow managed to pull off an economic miracle. Makes our current inflation-fighting tools look rather tame in comparison. "Sorry, best we can do is nudge interest rates up a quarter point at a time.