As the saying goes, one should reflect on himself three times per day for self-perfection. I think I have been staying up too late every night for so long. Mother always complains that I am unable to get up early to report to her. Mother is an early riser and never goes to bed late. That may be one of the reasons why she still keeps healthy at such a senior age. When we lived together, I would be wakened as soon as she got up every morning. Although I can have a good sleep every night, I'm sure if I continue to delay my retirement for night, my health will be greatly affected. Once I realized my bad habit, I must do away with it immediately. As Ms Qu pointed out, the irregularity of people's life in modern era threatens the health of human beings today. It's  more important to make our life conform with the regularity of nature than to take exercise.