Sumantra was a man of worldly wisdom. Never tell a truth that is not pleasant. It is a keynote instruction. As such, though Sita had uttered the words in her sorrow, he did not repeat them before Kausalya, as it would increase her sorrow. Therefore Valmiki says: Avoiding the reference that had slipped off his lips through inadvertance, Sumantra began to speak agreeable words that brought delight to the queen.
Sumantra consoles Kausalya 2.60.1-23
Sumantra was a man of worldly wisdom. Never tell a truth that is not pleasant. It is a keynote instruction. As such, though Sita had uttered the words in her sorrow, he did not repeat them before Kausalya, as it would increase her sorrow. Therefore Valmiki says: Avoiding the reference that had slipped off his lips through inadvertance, Sumantra began to speak agreeable words that brought delight to the queen.