Have you ever found you want more kinds of cosmetics when you are interested in make-up? Have you ever kept yourself thinking of how to earn more money to buy a bigger house even if you've already have a comfortable one? Have you ever recognized that you are thirst for creating some curious or advanced knowledge in your own territory? It is certainy that little of us hasn't the similar experiences which contribute to my viewpoint that people are never satisfied with what they have and they always want something more or something different.
The primary reason why I insist on the above statement is that human beings have needs in several hierachies which can't be satisfied all. As maslow's hierarchy of needs goes that people have physiological needs, safety needs, belonging needs, esteem needs and self-actualization needs. In the levels of the five basic needs, the person does not feel the second need until the demands of the first have been satisfied, nor the third until the second has been satisfied, and so on.
Another reason convinced me of the opinion why people are difficult to satistied and always in need of more things or particular things is that curiosity is a kind of human nature which accurately exists in most of humans. More or less, it is one of the features to distinguish human beings from animals. A typical case in point is that human will feel curious about why the apple fall to the ground but not the sky and take a deep thinking of it. Thinking, the manifestation of curiosity, is an ability which doesn't shared by any other animals.
Last but not least is that such kind of behavior of human boosts the progressing of society. It explains why scientists keep on searching for more high-tech technology and advanced skills, probes how the internet speeds up globalization, brings negative and positive views towards life. Not only is this disatisfation stimulates the inspeculation for the unknown world, but also imspires some imaginations to fulfill other theories.