Happiness is not something one "gets" by things happening...happiness is something one has to create!
The level of happiness depends on the person, not on circumstances.
What they are talking about is joy, and joy is fleeting.
Although, I think the level of happiness is very low in people here...maybe because they do not know that it is up to them to create the level they wish to have. If they make it dependent on outside circumstances...well...then it does look rather dreary.