If I have a paper book of passwords at a desk in an open office environment, sure, that’s bad. If I have a paper book of passwords in a locked safe in a house, and there is perhaps a large German Shepard and multiple able-bodied adults living in that house, I’d say my password book is relatively secure.

Besides, actually remembering your passwords is a security flaw, too. Memorable passwords are naturally less random, and if the password is in my mental memory, an attacker can compromise my password by smashing me over the kneecap with a heavy wrench until I tell them. If I don’t even know my password, that’s probably bad news for my kneecaps but slightly more secure overall.