Yes, indeed, it is from human activity depends his future position in the world, in the society. It is from the intellect, mind, and labor activity, which will determine his future destiny, and therefore, and happiness. Life is a great science, which I think is not less important than all the rest. And if you do not learn the highlights and the Golden rule of life, the collision with the problems very seriously can influence the further existence of the person, and consequently, on his happiness. This collision may lead to fatal, fatal error, fully abusive and possibly destructive person, the consequences can be very irreversible.
I think that apart from labour and mind, a person needs to have a purpose in life, that is, the main label and the level that would need to be achieved in the process of existence, to know where you can still find happiness.
Of course, a full, happy life is impossible without self-realization of man. After all, happiness to deal with the fact that man is capable of, what corresponds to his taste.
People Slaven what life imprint he has left in the history. For example, doctors are thousands of cured returned to the lives of people in the writers are immortal Lite - ратурные wealth, artists are brilliant paintings, which amaze and fascinate mankind for centuries. For them it is a great happiness, because their labour they were able to bring people joy and unforgettable pleasure.