What re the circumstances that make humans unhappy and disillusioned with life?

Human beings become unhappy and disillusioned with life as they come to observe the banality of their own existence. The dearth of noble natures, of gloomy days and unhealthy ways bog down the human spirit. It brings a sense of despondence because the search for beauty amidst that gloom and monotony becomes doubtful. One begins to wonder if the exercise of trying to find beauty in this world is a worthwhile quest or not.