A fool suffers, thinking,

"I have children! I have wealth!"

One's self is not even one's own.

How then are children? How then is wealth?

--Buddha, The Dhammapada, verse 61

Buddha said that all things are like dreams, like illusions, and like a mirage that appears to be water but is not water. While things appear to exist from their own side, independent of our mind's perception, independent of the label we give them, and fixed, nothing exists in that way. Our self, our children, our wealth exist as mere name, mere label, and are impermanent. Being impermanent, eventually they change; our children grow up, our wealth changes, and our body changes. If we are attached to the way things used to be, we will suffer. If we understand that the end of rising is falling, the end of fame is obscurity, the end of meeting is parting and the end of birth is death, we can be a little more relaxed when things change. The wisdom of impermanence encourages us to accept things as they are and to enjoy the present moment. This story from Buddha's life that illustrates this idea:

Buddha and a group of monks, his followers, were eating lunch together when a farmer, very upset, ran up and asked, "Monks, have you seen my cows? The Buddha asked him, 'What happened?" and the man said, "Monks, this morning all twelve of my cows ran away. And this year my whole crop was eaten by insects! I don't think I can survive so much misfortune, I want to kill myself."" The Buddha said, "Sir, we have not seen your cows. Perhaps they have gone in the other direction." After the farmer went off in that direction, the Buddha turned to the monks and said, "Dear friends, do you know why you are the happiest people on Earth? You have no cows; you have no crops." We think our 'cows' are essential for our happiness. In fact, they may be the obstacles that prevent us from being happy is we are overly attached to them, because all things are impermanent and eventually we are parted from them. Release your cows, knowing they are impermanent, and become a free and easy person. Release your cows and you can be truly happy.

References:

The Dhammapada, by Buddha. Translated by Gil Fronsdale. Shambala, Boston and London, 2011, pp. 16

Great Treatise on the Stages of the Path to Enlightenment, by Je Tsongkhapa, Volume 1. Pagesare 167, 184. Translated by the Lamrim Chenmo Translation Committee. Joshua Cutler, Editor-in-Chief, and Guy Newlan, Editor

Great Treatise on the Stages of the Path to Enlightenment, by Je Tsongkhapa, Volume 3. Page 1263. Translated by the Lamrim Chenmo Translation Committee. Joshua Cutler, Editor-in-Chief, and Guy Newlan, Editor