So, since this seems to be relevant im a CISO myself. And i would definitely not agree with everything in this letter. Personally, i think the worst part about it is handling a low probability as something that's not gonne happen. Thats, especially in IT-Sec, one of the worst practices. To take on point as example - the "never scan public QR codes". Apart from the fact that there have been enaugh exploits in the past…
If you are an online service provider, sure. Low probability means it's going to happen, especially as you scale with users.
For a small business IT team? You can't keep a clean sheet, the strategy is to reduce the probabilities of an incident and reducing its damage, but it will never be zero, if only because you have non-technical users that need to do actual work.
p(incident) is just yet another variable you need to do tradeoff engineering on, and obsessing over reducing it to 0 will probably compromise other tradeoffs like ease of use of the system.
It's a special case of ironic when in an attempt to get a specific variable to 0 (which is impossible with most variables anyways) you end up compromising that specific variable. So if you force users to use lots of passwords and password managers and MFA, and limit their capabilities, they end up circumventing your security systems and advice, so they introduce an issue (but of course it will be the users fault, and not the CISO's fault, their job is secure).