In crypto, the private key, and the seed phrase that can regenerate it, is the only thing that proves ownership of your funds. There is no central company holding a master copy and no password reset button. If you lose the key and any backup of the seed phrase, access to the funds is typically gone for good.
This is a direct consequence of how self-custody works. The same design that stops anyone else from controlling your funds also means no one can restore them for you. Funds are not deleted; they simply sit on the blockchain, permanently locked because no one can produce the key needed to move them.
The practical takeaway is that prevention is everything. Backing up your seed phrase carefully, keeping it offline, and storing more than one copy in safe places is what protects you. With custodial services, by contrast, the company may help recover access, which is one of the trade-offs of that model.