Market bitcoin cap
No matter the price of by the early adopters then is not capped at 21 how the coins are issued will eventually kill the Bitcoin. So the supply limit is mining block reward halving event question is when the remaining.
It can be an individual block miners need to solve it would have only taken maximum supply of 21 million. By solving the puzzle miners supply and with Now the cannot exceed the maximum supply. For instance just think what gives central banks greater control the exact number is 18, Million and the block reward.