terror management theory.

Haha Wikipedia: 

According to terror management theory (TMT) neuroticism is primarily caused by insufficient anxiety buffers against unconscious death anxiety.^[32] These buffers consist of:

1. Cultural worldviews that impart life with a sense of enduring meaning, such as social continuity beyond one's death, future legacy and afterlife beliefs, and
2. A sense of personal value, or the self-esteem in the cultural worldview context, an enduring sense of meaning.

While TMT agrees with standard evolutionary psychology accounts that the roots of neuroticism in Homo sapiens or its ancestors are likely in adaptive sensitivities to negative outcomes, it posits that once Homo sapiens achieved a higher level of self-awareness, neuroticism increased enormously, becoming largely a spandrel, a non-adaptive byproduct of our adaptive intelligence, which resulted in a crippling awareness of death that threatened to undermine other adaptive functions. This overblown anxiety thus needed to be buffered via intelligently creative, but largely fictitious and arbitrary notions of cultural meaning and personal value. Since highly religious or supernatural conceptions of the world provide "cosmic" personal significance and literal immortality, they are deemed to offer the most efficient buffers against death anxiety and neuroticism. Thus, historically, the shift to more materialistic and secular cultures - starting in the neolithic, and culminating in the industrial revolution, is deemed to have increased neuroticism.^[32]

https://en.wikipedia.org/wiki/Neuroticism