Your brain is wired to engage in an endless pursuit of achievements. Take for instance: you spend your whole life trying to get a laptop. Then you get the laptop; a sleek Dell Notebook. But it does not take long, however, for you to start wanting a MacBook. Suddenly, your Dell does not matter anymore. Nevermind that it was everything you wanted a year ago.
We like to call it "growth," and perhaps it is. But do not forget to remind yourself how much you wanted what you now have and allow yourself to be happy.