When Karthik comes to Singhania Mansion, he tells Naira that will she understand him. He speaks, he his heard by everyone in that room, but the only one person who understands him is his girl, his Naira. Only she realizes the hidden meaning of all his words.
When he said that they couldn't oppose dadi everytime, while other's thought he was okay with the name change, she understood it meant something more.
When he said he would do the right thing, everyone was pretty sure that he was okay with the name change, only she understood that he would do the right thing.
When he said he would do what would please more people, to everyone it seemed like he talked about pleasing his dadi, only she understood he actually wanted a way that would please everyone, or almost everyone.
It is amazing how he speaks to all, not once does he lie, yet the truth is heard by one.