And I agree that brain is the best place, although I could tell you a story. I created a new account at the new bank, because they had a super high interest rate. I was assigned a temporary customer id and password, which I had to (both) change immediately after logging in to my internet banking account. So I picked a crazy paranoid password and id and saved it to my brain. Week after, my debit card arrived via snail mail with instructions to activate it in IB.

But I forgot the password. So I called the hotline, where they asked for my customer id, which I forgot too

It’s certainly arguable, but I think it’s still better to write down a password on an offline media (which would require physical theft) than to choose a simple password, as simple passwords could be hacked by literally anyone out there, whereas your offline notes can only be accessed by a rather tiny group of people (if at all).

But we do agree on the fact that the brain is the best place to store a password

1. They forget it, restore it and change it to something simple
2. They write it down somewhere

So I think that a better approach is to use whole sentences as passwords. Even simple sentences like “My wife’s name is ..” are immune to dictionary attacks, bruteforce attacks and rainbow tables.