There is no ghost so difficult to lay as the ghost of an injury.

Smith’s metaphor treats a past wrong as a “ghost”: something intangible yet persistently present, returning unbidden to trouble the mind. To “lay” a ghost is to put it to rest; the line suggests that injuries—whether suffered or inflicted—are among the hardest experiences to settle internally because they keep reanimating memory, resentment, shame, or a desire for redress. The remark also implies that time alone does not necessarily exorcise a grievance; it may require forgiveness, restitution, or a conscious reframing of the event. In a broader moral sense, the quote warns that harm has long aftereffects, haunting both private conscience and social relationships.