What is the origin of the idiom "rub salt in the wound" and when to use it?

The idiom "rub salt in the wound" originated from the literal act of adding salt to a wound, which is known to cause intense pain and discomfort. Figuratively, the idiom is used to describe a situation where someone does something that worsens another person's suffering, distress, or disappointment by highlighting or emphasizing their misfortune or failure.