There are also some other reasons. Most important of them is the desire to be needed, I think. We understand how important can be the results of our work and it helps us to overcome the difficulties we can face during our work. Another reason is communication. All people want to have friends and work is the place where we can meet friends with similar interests. And the last but not the least reason is pension, I sppose. We have to work now in order to get retirement payments when we are old.