Two reasons. It is all about the pressure of life and work. When people are at the young age, all what they need to think about is study only. They have to stay focused on their academic performances. They are not suffering from heave pressure actually. After grow-up, things changed. No.1, the burden of life. Which in my consideration, has got to do something with money, include financial support of a family. Apparently, this is the main reason that ordinary people like to miss their childhood. No.2, the working pressure is the center behind it. When we step into society, a decent job means everything. Then we would try to work hard on it. Too much desire and lots of ambitions at work. So, I think that millions of people would miss their simple and naive life in their childhood. That is it.