Systems, like functional code, can seem perfect in isolation. Everything is accounted for and it's provable. Beautiful! Applied to any useful purpose, though,

Systems, like functional code, can seem perfect in isolation. Everything is accounted for and it's provable. Beautiful! Applied to any useful purpose, though, there are externalities and there is the unexpected. If you include those externalities in your model, you not only have a more complicated model, but you probably have an even larger surface of externalities.