In a literal sense, margin is the open space circumscribing the writing on a piece of paper.  It designates the space that the writer is not supposed to write in.  It is intended to create a tidy boundary that contains the content of the rest of the page.  Without margins, the page would feel overcrowded, overwhelming, confusing, and possibly illegible, even if filled with lots of good content. Margins in life serve the same kind of purpose – to keep the busyness and fullness and necessity of life (all of which might be very good and important stuff!) from overflowing beyond its proper place and invading the open spaces that allow such valuable work to be sustained.