Why do we feel that being rich means having a lot? I think it is because being rich means you have a lot you can do. The human species and anything alive in general wants to move around and express its existence. It is an innate characteristic of living organisms to experience and share their liveliness.
If you think about it, what else can we do? What else can we feel suppose to do? Not moving, dreaming or expressing is the same as not living life and not being alive.
Think about the fear people have for getting stuck in an elevator compared to being lost in a desert. The setting that an elevator provides is very limited. It closes in your minds boundaries. There are only so many things you can do to try and get out before you have to accept the limits.
A boxed in mind is a frightful thing but the resulting fear also has a positive effect. It drives us to explore, gather and grow. It causes us to experience our lives by working productively and using its fruits to color our lives.
Take for example the acquisition of land. Everyone aspires to own a place where they can live themselves out. Where they can plant and build and discover nature and its laws.
Since birth, our innate tendency is to look for things to keep us busy. When we sleep our dreams keep us busy. When we lounge our thoughts keep us busy. Most of the time there is no knowledge of why we stay busy. We work to get food, to keep on working. Very appropriately the Bible refers to this endeavor as a chase after wind.
Thinking about it in this light might make one wonder why we improve, work on self-development or inner growth. One answer would be, it is our journey. Another would be that as long as there are stimulates available our minds will pursue them!