The quote from Mark Helprin's "A Soldier of the Great War" suggests that reason alone is not sufficient for absolute understanding or action. It highlights the idea that reason relies on fundamental beliefs or assumptions, known as postulates, which cannot be proven yet are critical for the functioning of logical thought.

This notion underscores the limitations of human reasoning, revealing that our rational processes are built on unprovable foundations. As such, while reason guides our decisions and understanding, it is ultimately constrained by these inherent postulates that we accept without proof.