Due to avidya or ignorance of our real nature. Not only we mistake the impermanent as permanent but also make further mistakes such as mistaking the impure as pure, the painful as joyful and the non-Self as the Self. This is what Patanjali, the great teacher of Yoga says, “Ignorance is taking the non-eternal , the impure, the painful, and the non-Self for the eternal, the pure, the happy, and the Atman or Self.
If we look at this phenomenon of searching the permanent, we will find that the search for the permanent is actually not for the permanent world but the permanent Self. We seek something in us that remains eternally secure, eternally unaffected and ever blissful. We search for this Eternal in various ways in the external world but fail. First the search begins in the world of senses, or sense pleasure but ends miserably. As Soren Kierkegaard, a 19th century proponent of existentialism philosophy, wrote in his Sickness Unto Death : In the bottomless ocean of pleasure, I sounded in vain for a spot to cast anchor. I have felt the almost irresistible power with which one pleasure drags another after it, the kind of adulterated enthusiasm which it is capable of producing, the boredom, the torment which follow.
Then, the search turns to the world of ego satisfaction, to the pursuit of power, fame and name. Though sanatana dharma accepts desire for money and all legitimate desires (artha and kama) as part of four purusharthas or goals worthy of striving for a human being, they are only considered steps to something deeper, yet more lasting. No one wants money as such but wants it as a means for obtaining happiness. Money has only an instrumental value and is not intrinsically valuable. True joy comes from discovering the real nature of Self, which is eternal and joyful.
Pure, eternal joy and peace are to be found only in union with the Atman. Our ignorance debars us from that union, but the dim, confused longing for happiness remains. So we are driven to seek it in the eternal external world. We are forced to accept wretched substitutes and to try to persuade ourselves that they are genuine and valid. Instead of eternity, we cling to what seems relatively enduring. Instead of purity, we value what seems relatively pure. Instead of true happiness we hold to what seems temporarily pleasant. But our satisfaction, also, is short-lived. The strongest tower falls, the most beautiful flower withers in our hands, the clearest water turns blackish and foul. Ignorance has betrayed us, as it always must. Yet, as we turn sadly away our eyes fall upon some new object of sense attachment and desire. And so the hopeless search goes on.
As If squarely meeting this search for the eternal the Svetashwatara Upanishad says:
“Only when men shall roll up the sky like a skin, will there be an end of misery for them without realizing God.”
In other words, it is impossible to find the eternal in that which is changing. Just as if is impossible to roll the sky like a skin or a cloth, so also it is impossible to become joyful and ever satisfied, not knowing or realizing the atman, which is eternal and indestructible in nature.