This is the 475th most frequent Japanese word.
なぜ
"Why"
In this sentence, 'なぜ' introduces a question asking for the reason behind someone's action of returning early.
なぜ君はそんなに早く帰ったのですか？
Why did you return so early?
In this question, 'なぜ' seeks the reasoning or justification behind the perception.
なぜ、今がその正しい時だと思うのですか？
Why do you think now is the right time?
Here, 'なぜ' is used to express the curiosity or question about the reason or cause for the described condition.