"You fail again?"
Translation:Bạn lại thất bại?
No because that would transform the sentence into an imperative meaning "fail again!"
So from what little I know, there are half a dozen particles (like không, ư, à) that can be used to make a declarative sentence into a question. Why don't any of them apply here? Elsewhere in this thread, it's implied that the position of "lại" in the sentence somehow makes it a question, but I'm not sure I understand. Em không hiểu!