When you hit the "start" button on your washing machine, it starts washing clothes, even if there are no clothes inside. It doesn't know if it's empty or not, nor does it care. Nor can it care. It's a simple machine organized programmed to behave in a specific way given a certain input. If it deviates from this programming too often, it gets discarded and replaced with a more reliable model.

I believe the analogy is clear.