Ask why a facility went dark and the answer is usually a fault somewhere small that propagated somewhere large. Capacity was adequate; selectivity was not.
Discrimination has to be proven
Protection coordination is a study, not an assumption. Relay settings drift, equipment is replaced with non-identical units, and networks are extended without revisiting the scheme. Any of these can silently break discrimination that was correct on the day it was commissioned.
Maintainability is part of resilience
A facility that cannot isolate a section for maintenance will eventually defer that maintenance. Designing isolation and redundancy in from the start is cheaper than the outage that deferred maintenance causes.
Revalidate on change
Treat the coordination study as a living document. Any material change to the network — added load, replaced device, new feeder — is a trigger to revalidate it.