I don't think we ruined our ability to think about things, this was a failure to build a reasonable system. It's just basic planning and trying to consider possible faults. If the only way you will be informed of a potentially deadly situation, a sensor reading out of range - that affects human health - is it okay if it is only via email???

What if the person who reads the email was gone that day? What if they forget to read it? What if the email system is down? What if it was lost? This is just careless and bad design.

At the very least you need a backup notification, like say a warning siren or noise at the pool? Probably you don't want to do that casually because "it could scare people".

It's not some tricky thing where you had multiple ways to detect it, giving some redundancy. Same thing if it was a text message only or a phone call only.

This is a poor safety design with a single failure mode on the notification.