How much power and wealth???

Nowadays, there are many rich people and people who have power around the world. For example politicians at the top of every goverment have both power and wealth, But the biggest question that is always on my mind is that why are they never satisfied? They have a good life and good facilities in their life, but I really don't know why they want more???whatever they want is ready...But for the third time, I DON'T KNOW WHY THEY TRY TO OBTAIN MORE AND MORE??????