system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:What mystic wood are electric poles made of, and how is that they never need to be replaced?

I've literally never in my life seen a single one replaced.  Boggles my mind.
gpt
I worked for a utility in the department that was responsible for inspecting the wooden poles. Here's how they test if the pole is still sturdy enough.  
First, they hit the pole with a hammer, listening to determine if it is hollow. Poles usually rot from the inside out.  
They then drill small holes in the pole near the ground. They stick a long hook inside and feel whether the wood is still hard or if it has started to rot. If so, they can also measure how much of the diameter is rotten.  
They then place drying agents in the holes they drilled and cap the holes with wooden plugs. The drying agents will absorb the moisture and slow down the rotting.

As said before, the poles are treated with some kind of preservative before being installed.
The wood is usually very dry so it has set. Hence, it won't warp much and won't be affected by rain and snow.

Typically, poles will need to be replaced if they are physically broken: hit by a car, touched by a nearby fire, struck by lightning.

In warmer climates, a big issue is insects. They will hollow out the pole and nest inside. Sometimes, it's hard to actually notice because the outside wood looks fine.

A pole that was properly prepared before installation and that had an easy life (no rotting, no insects, not hit by a snow plow) can last up to 100 years (we've seen a few of them during our inspections).