Some twentieth century thinkers spent considerable time trying to understand what, exactly, one can know about the world. They thought that the fundamental basis upon which our knowledge of the world rests is suspect, based, as it is, on imagined truths originating from cultural orientations that define reality in terms of conceptual dualisms. Human inclination was to seek a secure ground of being in God or, perhaps, science that could provide reliable answers in dark times of stress and desperation. Such grounding led to unverifiable premises that produced false assumptions about the nature of the world.
A number of these deep thinkers dismissed the reliance on the eternal and infinite as being outside the realm of finite human understanding. All that can be known for certain, they thought, are the facts that exist in this world. These guys thought a primordial ground of being as disclosed through conventional world views was not to be found. An honest search would instead reveal an abyss, a nothingness beneath the cultural veneer. To live an authentic life, they believed, one must man-up, face uncertainty, tempt fate and step away from the safety of familiarity.
Other philosophers of the time thought a subjective ground of being could be found. Realizing the freedom to do what one chose depended upon a spiritual component to lift such a person beyond causal necessity. This ground of being will be personal and dependent on a belief in an existence beyond factual knowledge.
I have to say I admire these great thinkers living as they did through difficult times, unstable finances and psychological angst, who spend so much time and energy pursing ideas that provide us all the opportunity to at least contemplate how we can live our lives authentically.