It is estimated that out of the total supply of 21 million bitcoins, approximately 3 to 4 million have been permanently lost, accounting for approximately 14% -19% of the total; Based on the current price of approximately $90000 per piece, its value is estimated to be between $195 billion and $260 billion. Common reasons for asset loss: Lost or forgotten mnemonic words or private keys Hardware wallet malfunction and no backup available Accidentally sending assets to the wrong chain (e.g. sending BTC to ETH)