The phrase has been repeated in the sector for over a decade: not your keys, not your coins. It is technically accurate. It is also incomplete advice presented as complete advice.
What self-custody protects against
Counterparty failure, which is not a hypothetical risk. Exchanges have collapsed, frozen withdrawals, and been found to be operating with less than they claimed. In every one of those cases, users holding their own keys were unaffected.
That is a real and demonstrated benefit. The history of the sector is substantially a history of intermediaries failing.
What it does not protect against
Yourself. Self-custody moves the entire risk of loss onto one person with no recovery mechanism and no support line. A lost recovery phrase is permanent. A phishing signature that drains a wallet is permanent. There is no reversal, no dispute process, no insurance.
The failure rate from user error has almost certainly exceeded losses from exchange failures, though nobody can measure it because the losses are silent.
The practical requirements
Doing it properly means a hardware device, a recovery phrase written on something that survives fire and water, stored somewhere that is neither your home nor a place anyone would look, and a tested recovery procedure.
It also means an inheritance plan, because the same properties that make a key secure make it inaccessible to your family. This is the part nobody mentions and the part that has cost the most.
Who should actually do it
Anyone holding an amount they would be materially hurt to lose to a counterparty failure, who is willing to treat key management as an ongoing responsibility rather than a one-time setup.
Anyone holding a small amount, or unwilling to maintain that discipline, is probably safer with a regulated custodian – where the risk is a well-understood institutional one rather than an unbounded personal one.
The uncomfortable conclusion
Both options involve trusting something. Self-custody trusts your own operational discipline over years. Custody trusts an institution’s solvency and honesty. Choosing is a judgement about which failure you are better placed to prevent, not about which is theoretically purer.