When the Buddha taught that there are three characteristics of facts of existence. They are generally found in all that exists and so they can tell us something about the nature of existence. The three characteristics of existence taught by the Buddha are Impermanence, Suffering and Impersonality.
The Truth of suffering is the first of the Four Noble Truths [Chin.: sìshèngdì 四圣谛 | Sansk.: चत्वारि आर्यसत्यानि catvāri āryasatyāni] taught by the Buddha.
Developing insight into Suffering lead to greater compassion for other beings.
Venerable Shi Yong Hai [Chin.: shìyǒnghǎi 释永海 | 1952 - ]
Suffering is a fact of life which people can see for themselves. It is one of the three characteristics of existence.
Whatever is impermanent is also suffering. Everything which arises will last only for a time, then it decay and finally dies. Repeated birth and death is hard to endure, It disturbs one's peace and mind and is a cause of suffering.
Thus old age, sickness and death which are evidence of the impermanence of life are forms of suffering. Since people tend to cling to youth, heath, relationship and material achievements, the realisation that these are impermanent, cause anxiety and fears.
It is said that even the gods trembled when the Buddha reminded them that the heavens are also impermanent.
Understanding that suffering is universal and inevitable enables one to face the realities of life with calmness of mind. One will be able to cope with old age, sickness and death without becoming disheartened or desperate. It also encourages people to look for solution to the problem of suffering just as young Prince Siddhārtha Gautama did.
I have taught one thing, and one thing only, Suffering and the cessation of Suffering.
Buddha Words from Alagadduupama sutta
The Gift of Truth, which Leads to Wisdom, is the Greatest of All Gifts
Master Shi Yan Zhuo [Chin.: shìyánzhuó dàshī 釋延卓大师 | 1965 - ?]