"subjective" here doesn't mean "it's just made up and you can choose arbitrarily"
it means it depends on the subject (whoever we are talking about)
if you had 10 Bitcoin, what would you do with them?
The only answer is sell them - in which case why would there be a buyer?
And one day there won't be
This is (with minor caveats) true of US Dollars also
But not true of precious metal