That's not strictly true. If you're careful and imaginative, with moderate effort you can commit a fair amount of highly random data to memory. You just can't expect to change it every month.

This may be oversimplified, but it's the correct horse battery staple.

Eh, it depends, a random fragment of a very long poem for instance can be quite easy to memorize but at 80-90 words/300-400 characters long is pretty damn secure, doesn't even need to be written down then.

"muscle memory" helps here. People only need to refer to the scrap of paper for the first couple of weeks of entering a password.

Then that scrap can be securely stored somewhere else. (eg: In your "in case of death" box if you want people to have access when you die.)

What the? If you write it down, it's a bad password. Make it a pass phrase, make it long. And possibly store it in an encrypted password database, protected by a master pass phrase.

My password was randomly generated, has 85 bits of entropy and, it took me only a couple of days to memorize.

Hmm, hope you don't take many vacations