Yoga Sutras of Patanjali translated by Yogi Kalinath - Chapter 2, Verse 15
Pada 2, Sutra 15
Parinaama-taapa-sanskaara-duhkhair guna-vrtti-virodhaac ca duhkham eva sarvam vivekinah
The discerner (wise person) knows that due to the Sanskaras (subliminal activators), and on account of mind fluctuations (Vrittis) sparked by the material modes of Nature (the Gunas), all is suffering.
The nature of life is change. Everything is impermanent. Even conditions leading to happiness will not last and this include suffering also. Everything fluctuates in life including our own internal world as thoughts and emotions. Both attraction to pleasure including chasing after pleasurable experiences and aversion to pain and running away from the concept of suffering are forms of attachment (one positive and the other negative) that will give rise to suffering due to insatiable cravings, fear of loss and anxiety.
The issue is not with happiness, joy, things or people but in developing dependence upon them for our happiness and joy. The problem is in our unrealistic conscious or unconscious expectations of finding everlasting happiness and joy in circumstances, states, status, things or people. All of these change over time and are not permanent in their existence. Due to their temporary nature, they can only at best offer us relative happiness and joy. The ultimate fulfilment can only be experienced by, for and through the Ultimate, the Supreme Self, the Parama-Atman.