When a user loses his wallet details, I think it has the effect of removing money out of circulation. Hence lost bitcoins still remain in the block chain just like any other bitcoins. However, the lost bitcoins remain dormant forever because there is no way for anybody to find the private key(s) that would allow them to have access to the bitcoins and be spent again. I’m sure because of the law of supply and demand, when fewer bitcoins are available, the ones that are left will be in higher demand and increase in value to compensate. So I still wonder what then happens to those lost bitcoins, because I think since no one can have access to the private keys what about the developers of the blockchain app? Can the developers of block chain gain access to the lost coins and withdraw them from the lost account?