The drama "大唐狄公案" depicts a scene where a newlywed couple is forced to play a chess game on their wedding night. The loser of the game is required to be stabbed by the winner. Initially, the couple hesitates to harm each other and even tries to take the knife for themselves. However, they are later informed of each other's ungrateful behavior, which leads to their mutual anger and retaliation. Unfortunately, the specific reason for the couple's decision to kill each other is not provided in the search results.