Srimad Bhagavatam Canto 07, Chapter 07, Text 42

SB 7.7.42

sukhaya duhkha-moksaya
 sankalpa iha karminah
sadapnotihaya duhkham
 anihayah sukhavrtah
 
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
 
In this material world, every materialist desires to achieve happiness and diminish his distress, and therefore he acts accordingly. Actually, however, one is happy as long as one does not endeavor for happiness; as soon as one begins his activities for happiness, his conditions of distress begin.
 
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
 
Every conditioned soul is bound by the laws of material nature, as described in Bhagavad-gita (prakrteh kriyamanani gunaih karmani sarvasah). Everyone has achieved a certain type of body given by material nature according to the instructions of the Supreme Personality of Godhead.
 
isvarah sarva-bhutanam
 hrd-dese ’rjuna tisthati
bhramayan sarva-bhutani
 yantrarudhani mayaya
 
“The Supreme Lord is situated in everyone’s heart, O Arjuna, and is directing the wanderings of all living entities, who are seated as on a machine, made of the material energy.” (Bg. 18.61) The Supreme Personality of Godhead, the Supersoul, is present in everyone’s heart, and as the living entity desires, the Lord gives him facilities with which to work according to his ambitions in different grades of bodies. The body is just like an instrument by which the living entity moves according to false desires for happiness and thus suffers the pangs of birth, death, old age and disease in different standards of life. Everyone begins his activities with some plan and ambition, but actually, from the beginning of one’s plan to the end, one does not derive any happiness. On the contrary, as soon as one begins acting according to his plan, his life of distress immediately begins. Therefore, one should not be ambitious to dissipate the unhappy conditions of life, for one cannot do anything about them. Ahankara-vimudhatma kartaham iti manyate. Although one is acting according to false ambitions, he thinks he can improve his material conditions by his activities. The Vedas enjoin that one should not try to increase happiness or decrease distress, for this is futile. Tasyaiva hetoh prayateta kovidah. One should work for self-realization, not for economic development, which is impossible to improve. Without endeavor, one can get the amount of happiness and distress for which he is destined, and one cannot change this. Therefore, it is better to use one’s time for advancement in the spiritual life of Krsna consciousness. One should not waste his valuable life as a human being. It is better to utilize this life for developing Krsna consciousness, without ambitions for so-called happiness.
Srimad Bhagavatam Canto 07, Chapter 07, Text 41
Srimad Bhagavatam Canto 07, Chapter 07, Text 43