A seed phrase is an ordered sequence of common words — generated when a wallet is created — from which every private key in that wallet can be mathematically derived. Anyone holding the words can reconstruct the wallet on any device, anywhere, without needing the original hardware. It is not a password protecting an account; it is the account.
The order is part of the secret. The same words in a different sequence produce a different wallet, which is why phrases must be recorded exactly rather than approximately. It also means a phrase cannot be reset or reissued: unlike a password, there is no provider holding a copy and no recovery flow behind it.
This creates a security posture with no middle ground. Storing it too openly invites theft, since anyone who reads it can empty the wallet immediately and irreversibly. Storing it too privately risks the assets dying with you. Most catastrophic losses come from one of those two extremes rather than from any sophisticated attack.
Practical storage favors durable physical media in more than one location, protected against fire and water, with the location documented for your executor without the words themselves appearing in any document that becomes public. Photographs of a phrase on a phone, cloud notes, and email drafts are common shortcuts and each has produced real losses.