A group of people lost a large amount of money. There was one person in the group who was still happy, even though the others were miserable over their loss. The others asked him how he could be so happy while they were so sad.
He replied, "I'll give you an analogy. A person once came into a room where a few people were sleeping. The sleepers were dreaming nightmares and cried in their sleep. The person who was awake did not join them in their crying for he realized it was merely a dream. Similarly, I realize this world is like a dream. People upset over worldly matters are as in the midst of a nightmare. I am awake, and cognizant of how illusory worldly suffering really is."
(Pele Yoatz - Tza'ar; Rabbi Pliskin's Gateway to Happiness, p.246)