Since they were young, we can see that being unsatisfied is human natural behavior. We can see how children is never satisfied with the toys they had, teenager keep updating their gadget, woman is never satisfied with all the branded stuff they had, and man is never stopped reaching for a higher position in their office. Those are all the example of human dissatisfied behavior.
Once you reach what you want, you will start looking for something better. Once you reach what you want, you will start proud of yourself. Then, the next step is you think that you deserve for the better one. So, you start searching for the better one. The scientist doesn't stop doing all the experiment, The IT Companies never stop publishing the up to date gadget, and Windows never stop upgrading the better version.