Ecclesiastes 1:17 And I set my mind to know wisdom and to know madness and folly; I realized that this also is striving after wind.

Ecclesiastes 2:23 Because all his days his task is painful and grievous; even at night his mind does not rest. This too is vanity.

Ecclesiastes 2:26 For to a person who is good in His sight He has given wisdom and knowledge and joy, while to the sinner He has given the task of gathering and collecting so that he may give to one who is good in God's sight. This too is vanity and striving after wind.

Ecclesiastes 3:10 I have seen the task which God has given the sons of men with which to occupy themselves.

Ecclesiastes 3:11 He has made everything appropriate in its time. He has also set eternity in their heart, yet so that man will not find out the work which God has done from the beginning even to the end.

Ecclesiastes 4:8 There was a certain man without a dependent, having neither a son nor a brother, yet there was no end to all his labor. Indeed, his eyes were not satisfied with riches and he never asked, "And for whom am I laboring and depriving myself of pleasure?" This too is vanity and it is a grievous task.

Ecclesiastes 7:25 I directed my mind to know, to investigate and to seek wisdom and an explanation, and to know the evil of folly and the foolishness of madness.

Ecclesiastes 8:17 and I saw every work of God, I concluded that man cannot discover the work which has been done under the sun. Even though man should seek laboriously, he will not discover; and though the wise man should say, "I know," he cannot discover. (NASB ©1995)