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I trust fiat because my entire life I have been able to spend it almost anywhere.  That's all that matters for currency.  Can you spend it today and in the future?

People have evolutionary reasons to not just randomly try new things with no track record.  That's why gradual changes are so prevalent and it's tough to introduce revolutionary ideas.  Society and people through trial and error find a lot of things that work, and it doesn't matter if they understand why it works or not.  People tend to get angrier around red things, for example.  They don't need to understand it.  It just served us well for a while.  There are societal customs that don't make sense, but people aren't about to change them or even question them.

Now there are times when superior ideas do come about and take a while to catch on.  Usually it takes some set of early adopters to test it out and prove it works, then more get on board.  This is the case with almost any new idea that ever happens.  And a lot of the time, the better ideas win out.

So trusting fiat will work until it doesn't.  No one needs to know why Bitcoin is superior.  Only the early adopters do.  The rest will follow along once they see it works and see some tangible ways.  They don't need to know how it works any different than knowing how an internal combustion engine works when they drive their car or how structural engineering works when they drive across bridges.  They see lots of cars driving down the street and across bridges and figure that's good enough.