Bitcoin technology is impressive for just how many fundamental problems with money it solves. One advantage of bitcoin that is often touted is that it provides for final settlement of transactions.
Final settlement means that, once a transaction is mined and enough subsequent transactions have been mined as well, it would take an infeasible amount of energy to go back and reverse the original transaction. There is a well-known guideline that a bitcoin transaction can be considered final if five additional blocks are then added to the timechain following the block containing the transaction.
(For technical readers: With today’s mining hash rate of about 585 exohashes per second, the total work required to reorganize a block 6 blocks deep in the timechain would require about 2 million exohashes, demanding about 63 thousand terajoules of power. This is the equivalent of one thousand Hiroshima-sized atomic bombs.)
And so, the common wisdom suggests that after these six confirmations of your transaction, it is as good as etched in stone. However, this view is simplistic and fails to account for a crucial factor: privacy.
