S., a frank and intelligent man, told me as follows how he ceased to believe:-
He was twenty-six years old when one day on a hunting expedition, the time for sleep having come, he set himself to pray according to the custom he had held from childhood.
His brother, who was hunting with him, lay upon the hay and looked at him. When S. had finished his prayer and was turning to sleep, the brother said, ‘Do you still keep up that thing?’ Nothing more was said. But since that day, now more than thirty years ago, S. has never prayed again; he never takes communion, and does not go to church. All this, not because he became acquainted with convictions of his brother which he then and there adopted; not because he made any new resolution in his soul, but merely because the words spoken by his brother were like the light push of a finger against a leaning wall already about to tumble by its own weight. These words but showed him that the place wherein he supposed religion dwelt in him had long been empty, and that the sentences he uttered, the crosses and bows which he made during his prayer, were actions with no inner sense. Having once seized their absurdity, he could no longer keep them up.
~Tolstoy, quoted in William James, The Varieties of Religious Experience