This is just an effect that the director wants to express. The candle burned out and went out by itself. In order to go to America, Su Mei, who is indifferent, studied hard. When her candles were gone, she went to find someone else to continue reading. The director just wanted to create a chance for two people to get in touch for the first time, which also reflected the constant expression of the trend of wanting to go to America at that time.