Due to monetary policy that the Government have, they are freely to print and devalue fiat easily, even though we want to takeover and take care of this thing, we can't messed up with the Government in this kind of matter cause you know guys what will happen, we could end up in bars. Inflation is a disaster of fiat currency since the very first time, when things got their value and people started to trades commercial products.
Technically, fiat is not that useless, it is that the Government makes it looks and really useless because of their power creating more of it, Governments are worthless, in my jurisdiction.
Only the issuer makes it worthless or no value at all. They can demonetized it, or announced that a certain denominations will no longer be allowed as tender payments etc. Yeah, its the government that really makes it useless , they have the power to create and destroy it. Inflation weakens it, lower its value or purchasing power.