Why is AI our biggest existential threat?

Because we are not prepared for whatever AI will bring us.

For example, we kind of know what kind of problem North Korea is.
We kind of know what kind of problem Putin and Russia are right now.
We kind of know what kind of problem China might be now and into the future.
We kind of know our own problems here in the western world.

But, we have no idea what to look for at all if AI (Artificial intelligence) begins to stalk us.

Stalking is different than killing but killing might be a self driving car going off an overpass, it might be a medicine prescription that is incorrect so we die, it might be almost any food we eat processed in a way that slowly or quickly kills us. AI can be much more overt or much more subtle or anywhere in between. Or it could just be dust in the CPU that freezes the wheels on a freeway so you are hit by 20 to 100 cars behind you at 60, 80 or 100 mph when all cars are self driving.