As mentioned earlier, when Satoshi created Bitcoin, in addition to the decentralization of the system itself, it also defined its economic policy.
Perhaps Satoshi was a black jack player and believed the system win on the dealer if it did not exceed 21 and therefore chose this symbolic number; we'll probably never know.
The fact is that he decided to impose a maximum number of bitcoins that could be created and "cuts in production", called halving, to act on inflation: every 4 years the amount of new bitcoins put into circulation halved and the "production" of new units will end when 21 million are reached, so inflation will gradually decrease until it becomes deflation after the last unit is undermined.
It is often said that bitcoin - did you notice the small letter? - it is a rare asset, because there will only be 21 million units.
In reality, this is not the case.
We can define it as a " scarce asset" since a limit to its inflation, to the amount of "coins" that can be "minted", has been established within the protocol, but it is certainly not uncommon or rare. Bitcoin can be defined as a "scarce asset", because it has precisely one of the characteristics that make a good gain value: scarcity.
The famous 21 million bitcoins, which are not 21 anyway - approximating by excess will be 20999949.9769 in 2140 [18] - are only a useful convention to understand this limitation, in a jargon called total supply.
