Because they don't believe in higher powers.
Papal towels.
I don't use a round piece of plastic as a shift knob.
I can't believe this. What did he tell his atheist friend? You won't believe this.
That one doesn't believe in six before marriage.
An atheist. He doesn't really believe in himself.
Someone knocking at your door for no apparent reason.
They don't believe in a higher power.