Ecclesiastes 1:13
“And I gave my heart to seek and search out by wisdom concerning all things that are done under heaven: this sore travail hath God given to the sons of man to be exercised therewith.”
There is no remembrance of former things; neither shall there be any remembrance of things that are to come with those that shall come after.
I the Preacher was king over Israel in Jerusalem.
And I gave my heart to seek and search out by wisdom concerning all things that are done under heaven: this sore travail hath God given to the sons of man to be exercised therewith.
I have seen all the works that are done under the sun; and, behold, all is vanity and vexation of spirit.
That which is crooked cannot be made straight: and that which is wanting cannot be numbered.
Counter-Arguments
The strongest case that this verse does not belong in this theme.

Cross-References
“To every thing there is a season, and a time to every purpose under the heaven:”
“In the sweat of thy face shalt thou eat bread, till thou return unto the ground; for out of it wast thou taken: for dust thou art, and unto dust shalt thou return.”
“Behold, I have done according to thy words: lo, I have given thee a wise and an understanding heart; so that there was none like thee before thee, neither after thee shall any arise like unto thee.”
“There is one alone, and there is not a second; yea, he hath neither child nor brother: yet is there no end of all his labour; neither is his eye satisfied with riches; neither saith he, For whom do I labour, and bereave my soul of good? This is also vanity, yea, it is a sore travail.”
“I have seen the travail, which God hath given to the sons of men to be exercised in it.”