We don't necessarily need every case to be testable, and even so thoughtful use of occams razor or something can prevent the kind of exponential worst-case scen

We don't necessarily need every case to be testable, and even so thoughtful use of occams razor or something can prevent the kind of exponential worst-case scenarios that almost nobody wants. My problem is that contemporary software design seems to draw that line at a place that allows for few use-cases. It seems to be especially prevalent in modern enterprise stuff like Slack or Skype -- with the latter being a very good example of the old ways (e.g. original skype clients) regressing into the new ways (e.g. latest skype version).