Just came across this article today says that 4 million out of the total supply of 21 million have already been lost due to various reasons. The most popular reason are the HODLers who are holding it for quite long. These people have reduced the supply of bitcoins in market which has upsurged the price of bitcoin so much. Satoshi surely is the biggest HODLer himself.
Here is the article :
http://fortune.com/2017/11/25/lost-bitcoins/But holding bitcoin doesn't mean they are lost forever or out of circulation?
My immediate thought, they are not lost, they are just simply not in circulation at the moment. Lost would be those coins that can no longer be accessed by anyone. I would expect that to be a much much smaller number, probably around 1% of the 21m coins at most.
Actually there are some unknown numbers lost forever. As you could loose all your BTC holdings by forgetting password to your BTC wallet, and those coins are not be recovered... therefore there never are as many BTC out there as they are accounted as mined. One of disadvantages of decentralized aspect of all Cryptocurrencies.
In order not to lose the passwords for the wallets I keep bitcoins in online wallets. I am sure that it is more secure than storing your coins on a computer or on paper. I think that people themselves come up with challenges and then courageously overcome them. It seems to me that these 4 million coins is the money of those who do not believe in bitcoin and brought him back in 2010.