Maya (illusion)
An unmarried man is unhappy because he lacks a wife.
A married man is unhappy because he isn't satisfied with the wife.
A man with a good wife is unhappy because he lacks wealth.
A man with a good wife and wealth is unhappy because he lacks health.
A man with a good wife, wealth, health, and all comforts is unhappy due to lack of a son.
One who has all of the above still eventually becomes unhappy, dissatisfied, and angry for a reason he himself does not understand...
What does this show? It shows that one cannot get everlasting happiness through objects and experiences of the world. This is because the world is Asath (unreal). That which is unreal cannot give satisfaction. It is like the mirage of an oasis in the desert.
Just as the mirage of an oasis does not contain water and hence cannot quench the thirst of the thirsty desert traveler, any amount of worldly pleasure cannot make man satisfied and content. He will soon revert to his state of dejection and sorrow for a reason he himself doesn't comprehend.
"This world is like the image of an object reflected in the mirror."