। ॥ ५२३ ॥
In plain words
Because the love a man pours on his own son is as fierce as the love he has for himself; and because when the boy thrives he says, "I am thriving," and when the boy is gone he says, "I am gone" — therefore, on this ground:
Close to the Sanskrit
Because strong affection is seen toward one's own son also, as toward oneself; and because, when the son is thriving, 'I am thriving,' and when he has perished, 'I am lost' — therefore (this follows).