Ultimately—and I hope you’ll forgive me for going philosophical—in #Bitcoin, ownership is knowledge, and security is measured in time.

Knowledge can either be kept in one’s head or encoded in the world. One can encrypt information, but as you rightly point out, now you have the decryption key to store as well.

You can write words down by hand, or save a plain text file, perhaps in a secret location. But the location is now knowledge that has to be stored, and we’re right back where we started—memorizing secrets.

Because ownership is knowledge, exclusive ownership demands secrecy. But a secret written down can be discovered. Therefore the only way to exclusively own Bitcoin is to keep some amount of knowledge exclusively in one’s own head. Any configuration in which all of the knowledge is encoded in the world is exploitable.