https://marco.org/2007/07/29/in-order-to-be-certain-that-god-doesnt-exist-you
In order to be certain that God doesn’t exist, you have to possess a godlike mental capacity – the ability to be 100% certain. A human can’t be 100% certain about anything. Our brains aren’t that reliable. Therefore, to be a true atheist, you have to believe you are the very thing that you argue doesn’t exist: God.