"Turn to him the other cheek also" is often read only as a command about physical violence. The social world behind the saying adds another dimension: blows could function as deliberate acts of insult and humiliation in an honor-conscious society.
Jesus places the example among teachings about retaliation. The issue is not that injury is unreal, but that the disciple's response is not to be governed by the ordinary demand to answer insult with insult or injury with injury.