No question that fiat money can be mishandled. And the biggest problem fiat money can experience is hyperinflation, which reflects a diminution in value of the currency.
Way I see it, it isn't fiat money which is a problem. It is the underlying monetary policy. It is this in which people place faith. And yes, this is sometimes poorly managed.
But as you know by now, this isn't a problem with the USD which is highly valued these days, reflecting the fact that people place a good deal of faith in the performance of the Federal Reserve.