Blockchains are forgotten just as easily as any other data if the last backup is lost. Proof-of-work, however, makes it expensive to modify history. But it doe

Blockchains are forgotten just as easily as any other data if the last backup is lost. Proof-of-work, however, makes it expensive to modify history. But it doesn't change the fact that, in order to prevent data loss, the only solution is backups at multiple, independent locations.