>>509137767kek, this.
in theory, everything is backed up by something. fiat can be backed up by labor, or by military might.
another currency can be backed up by gold or something similar.
bitcoin can be backed up by trust in the system, or a desire to escape the fiat currencies.
but at the end of the day, all of it only has as much value as people are willing to assign to it.
if I say "no", then that's it. the deal won't happen.
the only thing that holds actual, undeniable value are the things you can turn your currency into. because I need food, I need a place to live, I might need medication and so on.
if you're smart, you try to keep as much of your wealth in material assets.