Bad money (when legally held at par) drives out good money (from circulation)

So if I have a crappy piece of paper or a gold or silver coin, I spend the piece of paper which will be worth less tomorrow and save the coin which will be worth the same (or if technological progress continues, slightly more)

Bad money doesn't drive good money out of existence

Some Americans do have hard money, it's just in their sock drawer rather than bank account or wallet