way in the folkloric Shahnameh has a happy end?

Of the most famous proverbs of Iranian people one is this: the end of Shahname is happy. This is used when something evil happenes for someone to give him a ray of hope. As it is obvious the Shahname ends with the attack of Arabs, the question is how the end of it is regarded happy? Some critics take the word "happy"as verbal irony, some other critics take "happy"'s original meaning: a critic relates the proverb to the triumph of Kaykhosro over Afrasiab. Some critics relates the meaning of this proverb to the fact of sharing candies by shahname singers (Naqaal) after their ceremony of citing the poem. A critic believes that the fact that Ferdowsi ends this great book was a kind of happiness. The article in hand believes this proverb refers to the reveng of Yazdgerd the third's murderer. Avenging the king's murder was sacred in Iranian thought, and this is seen in different parts of the Shahnameh. Therefore, since Bizhan by killing Soory takes revenge of Yazdgerd, they call it happy ending.