In his purport in the Srimad-Bhagavatam, 4.25.4, Srila Prabhupada wrote,
“In this material world there is a great illusion which covers real intelligence. A man in the mode of passion wants to work very hard to derive some benefit, but he does not know that time will never allow him to enjoy anything permanently. Compared with the work one expends, the gain is not so profitable. Even if it is profitable, it is not without its distresses. If a man is not born rich and he wants to purchase a house, cars and other material things, he has to work hard day and night for many years in order to possess them. Thus happiness is not attained without undergoing some distress.
“Actually, pure happiness cannot be had within this material world. If we wish to enjoy something, we must suffer for something else. On the whole, suffering is the nature of this material world, and whatever enjoyment we are trying to achieve is simply illusion. After all, we have to suffer the miseries of birth, old age, disease and death. We may discover many fine medicines, but it is not possible to stop the sufferings of disease or death. Actually, medicine is not the counteracting agent for either disease or death. On the whole there is no happiness in this material world, but an illusioned person works very hard for so-called happiness. Indeed, this process of working hard is actually taken for happiness. This is called illusion.”