Passage cross-references.

It is vain for you to rise up early, to sit up late, to eat the bread of sorrows: for so he giveth his beloved sleep.

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.

For all his days are sorrows, and his travail grief; yea, his heart taketh not rest in the night. This is also vanity.

Thus I was; in the day the drought consumed me, and the frost by night; and my sleep departed from mine eyes.

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.

The sleep of a labouring man is sweet, whether he eat little or much: but the abundance of the rich will not suffer him to sleep.

I applied mine heart to know, and to search, and to seek out wisdom, and the reason of things, and to know the wickedness of folly, even of foolishness and madness:

For he knoweth not that which shall be: for who can tell him when it shall be?

All this have I seen, and applied my heart unto every work that is done under the sun: there is a time wherein one man ruleth over another to his own hurt.