The world is always changing. Objects arise, wither and disintegrate. Mind, the instrument of perception, is also in constant flux.
We desire an object. Attainment of it produces happiness. However, the object changes. We change. Our own preferences change. What produced happiness does not produce happiness anymore. It produces suffering.
- A glass of wine was pleasant. A glass every day for sometime produces an adaptation in body and mind that requires increasingly larger quantities of wine to produce the same happiness. Eventually the liver is affected and results in palpable (and frequently inescapable) suffering.
- You are madly in love with a person. You are convinced of the life long partnership and the resulting eternal happiness. Years into marriage, the person has changed considerably. You have changed. The eternal happiness is now a series of battles with anguish.
- We desire and attain an eternal, immutable object (assuming such a thing exists). We control the mind such that it is stable and desires only the immutable object, then eternal happiness is possible. (Yoga: Desire the eternal, immutable object i.e. Puruṣa or the eternal Self. Stabilise the mind through practice and detachment.)
- We train the mind not to expect pleasure. We enjoy what comes. We can minimise suffering, if not attain eternal happiness. (Bhagavad Gita: Do the right thing and surrender results of action to God. Do not hanker after results.)
- We do not desire at all. Removing desire removes pleasure and pain. (Buddhism: Train the mind to regard everything as an illusion. Get rid of desire through renunciation or detachment.)
The grounds over which the search for eternal bliss rests are shaky.