Sometimes we spend a whole life (or a long period) chasing for something, and what will happen when we finally got it? Is there anything else worth fighting for? Or we are not supposed to reach the end of road, while find some other things in between.
Sometimes I was so busy and tied up, and when I was free, I have totally no idea what to do and feel at lost. We all need a purpose which never ran out. That explain why certain people refuse to retire, especially when you like your work.
We all need a moving target to keep us alive.