This is what makes fiat money dangerous. Unless it's backed by something with a long history of holding value, like gold, then the only reason for believing it will hold value rests with the government decreeing it has value. Unfortunately due to government tendencies this has been disastrous historically resulting in hyperinflation, rapid loss of fiat value, and people becoming poor overnight.
"Holding value" is a fallacy. Value is not inherent to gold, or anything else. The primary advantage gold had compared to other commodities is that it is difficult to counterfeit or arbitrarily increase its supply.
The reason that we use money is because it solves the double coincidence of wants problem, but at the cost of making it possible for the issuer of the money to consume products and services without first creating equivalent value. The first spender of newly-issued money gets to claim a portion of everybody else's deferred consumption for themselves.
It's not easy to avoid this drawback entirely because money has to somehow transition from a state of not existing to existing, so somebody is going to get to be the first spender.
Bitcoin addresses this by making the first spender work to build the network, and distributes new currency in a manner that is transparent and not subject to arbitrarily change. It's probably the best tradeoff we'll be able to achieve any time soon.
^^ this
