Whatever is highest and holiest is tinged with melancholy. The eye of genius has always a plaintive expression, and its natural language is pathos. A prophet is sadder than other men; and He who was greater than all prophets was a man of sorrow and acquainted with grief.
You find yourself refreshed by the presence of cheerful people. Why not make earnest effort to confer that pleasure on others? You will find half the battle is gained if you never allow yourself to say anything gloomy.