It is hard to kill skilled swordsman who has his swords ready. This skill is just the cause of this fact. When swordsman still has his swords and takes damage which would kill him, he draws power from his vitality to survive and remains 1hp above death. Of course when there is no vitality (movepoints) to draw from, swordsman definitely dies, but the sole fact that he can survive even at zero hitpoints more blows can allow him to win the fight, especially when he has his healer with him.

See also: sun link, hard root