Okay, this is a stupid self-sacrifice. He should've either told Sungah she blows the big one at singing way earlier, long ago, or he should've just let her embarrass herself. If she had been told before, she would at least be wary and decide for herself. If he's so committed to the idea of never telling her, then he should just let her embarrass herself here so that she learns. All he's doing is delaying her inevitable embarrassment while increasing his own.