system
Given the following post, respond as if you're commenting on Reddit:
human
Where does the endless flow of electricity come from in an electrical generator?

Mechanical rotation in a generator (fueled by flowing water, wind power, diesel burning etc) creates electricity. 
But the coil of wires and magnets rotating inside the generator is finite in mass, even though the electricity generated is endless. So where do the electrons/electricity come from?
gpt
Short answer: The electrons just wiggle back and forth, being pushed by the generator.

You might have the misconception that electricity works by sending electrons to whatever device uses them and that the device eats them up, like electricity worked the same as burning natural gas for your water heater. But it's quite different. The number of electrons in the generator and all the wires going to your outlet does not change, and the electrons are already there to begin with. The usefulness of electrons comes from their bulk motion. A generator is just creating the force to push those electrons back and forth, and when you make a complete circuit by plugging a device into your outlet then the force of that push is transmitted to your device.