More than enough people have, thankfully, pointed out the fundamental ... and horribly risky ... flaws in this advice.
So, if you’re not going to use a password manager … and, even without recent(ish) revelations of exploits of the most popular password managers, their efficacy is debatable for all kinds of reasons ¹ … the least risky course of action vis-à-vis passwords is not apasswordthatwillbecrackedinnexttonotimeatallbyverysimpletechniques but as follows:
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¹ Application corruption resulting in a failure to function correctly. Database corruption, meaning (unless you’ve backed it up ²) you’ll never be logging in again. Media corruption, meaning (whilst it might only be temporary) you aren’t logging in until you can copy your app and database back onto a new USB key (or whatever you were using). Loss of the relevant (second) factor (Yubikey, phone, etc.) … if you use such a device instead of a password manager app on a USB key … meaning you probably aren’t logging in again, ever, unless you find the item again — at best, as in the case of media corruption, you aren’t logging in here/now (and maybe not for a while until you can get a replacement and restore the backup ²).
² You made a backup, right. Right? A recent one. You didn’t keep meaning to but never quite get around to it because <whatever reasons you now regret, but basically because you were too lazy to>. What’s that you say … you were too lazy to? Well, now … there’s a surprise.
