Every inner state will naturally produce thoughts, even ascending to the heights of a philosophy, as direct emanations and justification of that state as truth, even final truth. The state becomes, particularly the more one becomes immersed in it, self-evident in its truth, it is that person's reality, and the thinker is not distinct from it.
Atheism is for instance the emanation of and simultaneously the attempt to justify a narrowed egotistical sense of being as truth. Whatever the inner state is tends not to be satisfied with itself simply as experienced reality due to, say, a certain way of life, but instead to be exclusive in proclaiming itself jealously as final truth. Atheism again so is the attempt of the petty ego sense of being to not shamefully feel itself as petty and narrowed down, but to actually proclaim this narrowed down state of being as the proud summit of reality - and as this gets pushed deeper in particular that particular individual's ego sense as final truth.