Bitcoin has a limited supply of 21.000.000 coins, with aproximatelly 18.500.000 being mined until now ( 88% of the max supply ).
However, out of the 18.500.000 Bitcoin that are supposed to be currently in circulation, about 20% hasn't moved in the last 5 years.
Out of this, a large amount of 1.100.000 BTC is considered to be the amount mined by Satoshi Nakamoto in the first few months of Bitcoin's existence.
Another important fact that decreases the actual amount of BTC in circulation is the loss of private keys?
While this might seem a bit odd today, I am sure you heard quite a lot of horror stories of people buying a few hundred coins when the price was really low just for fun and obviously forgetting about it until years later discovering in shock that if they would have been careful and kept their private keys they would be millionaires.
Altough it is obviously impossible to have an exact number of coins lost, it is safe to assume that the number is quite high.
What about you guys? How would you feel if you had bought 1000 Bitcoins years ago but lost your private keys?