Rostam and the White Div.
Pit fight! The final labour for Rostam is to find the White Div, leader of Arzhang and all the other demons. After killing a whole heap of the White Div's minions, Rostam descends into the pit where the White Div is hiding. It's pitch black.
He rubbed his eyes and peered into the pit's darkness, and made out a mountain there, hiding the pit behind its bulk. It was the color of night, its hair was white like snow, and the world seemed to be filled with its stature and breadth. It moved on Rostam like a black mountain ... Rostam's heart was filled with fear, and he thought that this might be one situation from which he would not escape. But he sprang forward like a maddened elephant and slashed with his sharp sword at the demon's trunk. ... the two locked together like an elephant and a lion. Each repeatedly tore flesh from the other's body, and the ground beneath them was turned to mud with their blood. Rostam said to himself, "If I survive today I shall live forever," ...
And that is that. The White Div knows he's going to lose his rep if Rostam wins, so psychologically the fight is over before it's even really begun. Then the Div is dead, and Kavus' sight is restored. Kavus is now free to keep getting himself into more and more foolish situations because of his lack of prudence and foresight.
When anyone talks about Rostam from here on, they all mention the fate of the White Div. If they don't, Rostam is there to remind them.