YOU SAID:

i don't know why i'm so handsome

INTO JAPANESE

私はなぜハンサムなのか分かりません

BACK INTO ENGLISH

I don't know why I'm handsome

INTO JAPANESE

なぜハンサムなのかわからない

BACK INTO ENGLISH

I don't know why you are handsome

INTO JAPANESE

あなたがハンサムな理由がわかりません

BACK INTO ENGLISH

I don't know why you are handsome