It proves it's a desired one. Which is a very important quality for a currency.

I learned different things in economics than. I learned about, scarcity, fungibility, divisibility, durability and transferability to be the main properties of a currency, not a desired factor of any case, afaik thats just a quality of humans, called greed.

Just because some people want something, doesn't make it a good currency. To stay in the same metaphor, I'd like to own the Nightwatch of rembrandt, just as many others do, still doesn't make it a currency or even gives it properties of 'currency'.

These properties are not mutually exclusive. But desirability is a required one for a good currency.

I agree that those other properties are important too.