Most of the reasons are "I do not know how to use AED", "I was not thinking about the existence of AED" and so on.
I will show you how to use again and important points again.
How to use the AED you want to check again
If the heart is convulsing "ventricular fibrillation" it will not be able to deliver blood to the whole body, people become stupid, both breathing and the heart will stop. If you find such a person, please ask someone around you to cooperate first. One brings an ambulance, one with an AED. Another person taps the shoulder lightly and lightly, please start vocal heart massage as soon as there is no response.