Probably a boring answer but I know my grandmother’s credit card information. I live with and help take care of her, so she doesn’t mind sharing it with me. Not like I’m planning to do anything nefarious, but I guess technically it could ruin her financially.
Writing passwords down isn’t that bad, actually. We humans are very good at securing little pieces of paper; just put the one you wrote your password on with the other valuable pieces of paper, in your wallet.
It’s “sticking the post-it note to the computer screen” that’s the problem.