Keys not coins

Bitcoin are never "in" a wallet, an app, or a device. Coins exist solely as UTXOs on the blockchain, replicated across every full node; what a wallet holds is keys — the ability to satisfy the spending conditions on particular UTXOs. "Sending" bitcoin does not move data from one device to another; it publishes a signed transaction that reassigns chain entries to new spending conditions. This is why a seed phrase restores everything on a new device, why the same funds are visible from any wallet software with the keys, and why custodial holdings are precisely defined: whoever holds the keys controls the coins.

Nuance: "Not your keys, not your coins" is the slogan form of this structural fact. Its precise content: a custodial balance is a claim on an intermediary's books, with counterparty risk, not UTXOs the holder controls. That is a factual description of the arrangement; whether custodial convenience is a reasonable trade is a judgment call that varies by user and amount.

Common misstatements:

• "I have bitcoin on my phone / on my Ledger." — Keys are on the device; the coins are on-chain. Device loss ≠ coin loss if the seed survives.
• "My bitcoin is on the exchange." — The exchange's keys control those UTXOs; the user holds an IOU redeemable at the exchange's discretion and solvency.
• "Wallets store bitcoin like files." — Nothing coin-like transfers between devices; only signatures and chain state change.