Comment by burnt-resistor

Not completely correct, nuanced, or comprehensive.

Direct lighting strikes cannot be defended against without extreme costs. This type of risk is generally extremely unlikely except for certain niche use-cases like equipment or facilities on tall peaks.

Transients from lightning (E2) nearby and distant nuclear detonations can be defended against, and often require additional protection of telco and internet entry points. Whole house type 1 SPD devices exist for residential applications. This is much more likely than direct lightning strikes, especially in certain areas and can be defended against for reasonable cost. The main issue of lacking it is the unseen, cumulative degradation of semiconductor components that lead to instantaneous or eventual failure, especially in high value devices like electrically-communicated motors in HVAC systems. There is no reasonable expectation of defense against a direct lightning strike even with type 1 SPD, and there are different types of lightning with vastly different amounts of energy. A positive strike direct hit will totally fry anything and everything.

What generally isn't defended against at all in any infrastructure or system except some military equipment is H/NEMP E1 (short duration impulses) or E3 (E3a or E3b; long duration surges larger than lightning) such as from unusual space weather events or nuclear blasts.