The first of the Four Noble Truths attributed to Buddha is life is suffering (dukkha).
But what is meant by this? Is every moment in life suffering? Am I in perpetual sadness?
Obviously, no. I am happy, or at least not sad at this moment. For most of my life I have been fairly happy and content. I can see that others also are not suffering or in constant pain.
What Buddha meant by this that at any moment we are susceptible to suffering. This susceptibility is what is meant by dukkha. Actual instances pain and happiness are “clues” to impermanence, unsatisfactoriness, and the self as an illusion.