For the most part, we go through our day contempt with the way things are turning out. We don't fixate so much on the positive things in our lives, but rather the things that troubles us.
So what makes anger, disappointment, frustration and all the things that troubles us stay around longer? It is the constant worry of not knowing the unexpected, which is why we choose to dwell upon this for so long.
And when something good comes along, then we take it for granted, or become satisfied for just a brief moment in time. It is not long before the happy feeling runs out, and before you know it, we return to our everyday normal lives, awaiting for the next great thing that will venture into our life and bring happiness again; but not fixated on when it will happen.