system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How are outdoor extension cords safe?

I just plugged in my Christmas lights. It's been raining today, so I made sure to thoroughly dry off the prongs first. But it got me wondering, what is it that makes an outdoor extension cord (and outdoor Christmas lights) safe to use in the rain and snow? Or is it actually not as safe as people tend to assume?
gpt
The cord itself is generally fine; it is well insulated with a thick, tough layer of rubber that prevents any problem.  As long as the cord is in good shape (no cracks or tears) and isn't abused (excessive flexing, tight bends, strong pressure, etc.) it is moisture-proof.
  
The problems come at the ends of the cords.  If those connections aren't well sealed against the weather, moisture can get in and cause a short circuit.   This will typically cause a breaker to trip before anything really bad can happen.