What did Martin Buber mean by drawing an ethical demarcation line each day?

Martin Buber’s ethical concept of the "demarcation line" refers to a daily moral practice of discernment within concrete situations. He proposed that one must draw this line anew each day to balance two competing imperatives: achieving the maximum amount of good possible while minimizing the necessary evil.1

This framework is rooted in Buber’s philosophy of the I–Thou and I–It relationships. The demarcation line serves as a guide for navigating human existence:

• I–Thou: Buber calls for this relation—characterized by mutuality and the fullness of being—whenever possible.1
• I–It: He acknowledges that we must settle for this relation—where others are treated as objects or tools—whenever it is necessary, such as for the purpose of human survival.1

Ultimately, this ethical stance reflects Buber’s commitment to a dialogical life, requiring individuals to actively and responsibly choose the nature of their encounters with others in every passing moment.12