I'm sorry if I say it wrong: I thought he realized the irony of his profession: Help Juve win the Scudetto at the expense of his old team. When he's on the pitch, he has to fight with all his heart. But when the battle is over, somehow he felt guilty. For a player who has won everything like Pirlo, there's no need to prove himself so he didn't cry because he's so happy. It gotta be something else.
