He who has 100 wants 200.

Rav Gifter asks why is it that Hashem tells us to be happy with the good that  he gives us.  Wouldn't it be a natural reaction to be happy.  The answer is that it is the natural reaction of man to want more.  In order for us to be happy we have to work on being grateful for the good that we are given.  At any given moment we are deciding 4 things: our thoughts, our feelings, our words and our actions.  By focusing on these, we can elevate ourselves and be happy.