Atheists strangely assume that those who believe in God believe in a fairy tale.
It's a postulation they arrogantly consider themselves qualified to make, as if they have mastered the totality of knowledge of life and of the universe – an intellectual hypocrisy they deem to be nowhere near as bad as the supposed fallacy of the believers' blind faith.
Yet, they sanctimoniously use said blind faith in their own God Complex or their Know-it-all Syndrome to appoint themselves as the new gods, and unseat the true God whom they pompously declare to be either dead or non-existent.
It's their equivalent of a coup d'état.
They actually fool themselves to believe there's no God by adhering to cockamamy theories like the Theory of Evolution and the Big (bada-bing-bada) Bang Theory, which they want humanity to believe are facts when in reality they're just that, theories (i.e., unproved assumptions or conjectures).
Worse, they do God's will every day, while invariably displaying a hostile attitude towards such will, even though they allow it to govern their lives.
Consequently, they come off as double-minded and quite unstable in their beliefs. It's a mental affliction psychiatrists call dissociative identity disorder.
However, we simply call it foolishness, though it is quite tinged with far more than intellectual hypocrisy. See How Atheists Do God's Will.