A dozen common words can restore an entire wallet with all its accounts across multiple chains. The design behind that is deliberate, and each part of it addresses a specific failure people make.
The words encode random data
A wallet begins with a large random number. That number is split into groups of bits, and each group indexes into a fixed list of words.
The words are not the secret in themselves; they are a readable encoding of the number, chosen so a human can transcribe them without error.
The word list is standardised, so the same phrase reconstructs the same value in any compatible wallet regardless of manufacturer.
The word list avoids ambiguity
Words were selected so no two share their first four letters, meaning a partial transcription is still unambiguous.
Similar-sounding and easily confused words were excluded, which matters when a phrase is read aloud or written by hand under stress.
The final word encodes a checksum, so a phrase with a mistyped word will usually be rejected rather than silently opening an empty wallet.
One phrase generates unlimited keys
The phrase is converted into a master key, and child keys are derived from it through a repeatable one-way function.
Because derivation is deterministic, the same phrase always produces the same sequence of accounts, so nothing beyond the phrase needs backing up.
Different chains use different derivation paths within that structure, which is why one phrase covers many networks and why restoring into the wrong wallet can appear to show nothing.
The phrase is the account, not a password
A password protects access to something stored elsewhere and can be changed. The phrase mathematically determines the keys themselves.
Anyone who reads it controls every account it derives, immediately and irreversibly, with no server to appeal to and no reset process.
This is why every legitimate wallet refuses to ask for it, and why any interface requesting it is doing something other than what it claims.
Optional passphrases add a hidden layer
Standards allow an extra user-chosen passphrase mixed into the derivation, producing an entirely separate set of accounts from the same words.
The phrase alone then opens one wallet and the phrase with the passphrase opens another, which is useful when disclosure may be forced.
The cost is severe: the passphrase has no checksum and no recovery, so a forgotten character produces a valid empty wallet with no indication that anything is wrong.