For example, several people have no money, but want to play a few games of mahjong, and then make an appointment for a card of poker to represent one dollar. Poker then generates a dollar value. The value it carries at the moment is the mutual promise of several people, and its function is to calculate the quantity.
In today's digital age, the immutable properties of the Bitcoin database accurately carry the mutual promises of Bitcoin holders, which can quickly calculate the quantity and transfer each other.
As a final note, Bitcoin is hard to come by, and if 21 million people buy one each, they will never be able to buy it again.
There are a million and one reasons why Bitcoin is valuable.
At first, it is the the first blockchain with a recorded Genesis onchain transaction of it's kind.
It is tagged as the modern day digital gold for which I am well aware you are informed about it.
It has a total supply of 21million which not all are in circulation. This makes it a scarce commodity and it's fractions more valuable than every other token or coin existing.
Bitcoin holders far much surpass every others existing onchain which makes it generally acceptable and some nations accept it as a legal tender.
Come to talk of it, the transaction Is very fast compared to Fiat transaction where you would have to wait for balancing of ledger before anything comes up to you.