Imagine a small town with 10,000 people. This town lives more or less apart from the rest of the word.
They have their own language, their own culture, and their own currency. It's a fiat currency, and it's purely electronic. People use it because to them it is just more convenient than using gold or silver. Their currency is totally decentralised, anonymous and it is called bitcoin.
Now, some terrible natural disaster occurs: an earthquake, a volcanic eruption, whatever.
Those ten thousand people have to leave their town and travel around the world to find a place to live.
They are dispatched in several countries where they learn the language and culture. But everywhere they go, they find that people use a currency that they consider inferior. Those currencies are controled by a bureaucratic elite, and there is no way to have financial privacy using these currencies.
So our small town people keep in touch between one another, and they keep exchanging the local currency against their bitcoins. Basically they never store any significative amount of the local currency, as they know it would be ripped by inflation. Instead, they only store their bitcoins.
When they need to buy something, they just sell some of their bitcoins to one of the small town people who has local currencies to get rid of. And then they can proceed to the paiement in order to buy stuffs.
You get my point, right?
Now, how many people are there on this forum already?