He had made the backup and promised himself he’d remember the passphrase. "It's simple," he had whispered to the empty room. "Unforgettable."
Incorrect.
Finding or recovering one of these files is often treated as a modern-day treasure hunt, as they can contain "exclusive" access to early-mined Bitcoin from the network's infancy. The "Exclusive" Appeal of Old wallet.dat Files
An old wallet.dat file is essentially a database of your Bitcoin keys and transaction history, often dating back to the early days of cryptocurrency. If you have found one, it may contain private keys for Bitcoin or various forks (like Bitcoin Cash or Bitcoin Gold). Essential Safety First