... As with most Ponzi schemes, modern fiat currencies are a matter of degree, belief, and tipping points.
There are always limitations in any system, and in paper money systems the debt must be balanced by real growth and investment, an organic growth that makes the rolling debt burden, which is really the basis of the money itself, sustainable and productive. That growth must be broadly based in order to support consumption from within the system itself, and this implies income commensurate with increasing productivity.
The failure of every fiat currency has been tied to the abuse of power, in the non-organic use of created money not to increase the productive growth of the economy, but to establish monopolies, cartels, speculation, and of course, aggressive war, all in pursuit of the outsized enrichment of a relative few who define themselves as an elite.
And human nature being what it is, all paper money systems have failed within a few hundred years. ...