Recently, retro music is popular in the domestic music industry. Even in the movie industry, remake or retro movies are made continuously. In this paper, we consider the reason of remake in the viewpoint of mathematics and show that there is a maximum number of lyrics, pictures, music, and movies that human can make due to the characteristics of digital contents. The time that human cannot make new lyrics, new pictures, new music, and new movies any more will be estimated. Therefore, artists will have difficulties to make new contents in the future, and human have to listen and see the previous lyrics, movies, music, or pictures in the future. This study will give a deep philosophical insight for contents industry.