I applied my mind to seek and to search out by wisdom all that is done under heaven; it is an unhappy business that God has given to human beings to be busy with. (NRSV 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. (KJV 1:13)
Ecclesiastes sees life as being basically troublesome. This view of life—as a waste of time and a burden—seems like it goes against most of the rest of the Bible. But when you consider that, in Genesis, God tells Adam and Eve that life after the Fall is supposed to be painful and a punishment, what Ecclesiastes is saying might seem like less of a contradiction.
Again I saw all the oppressions that are practiced under the sun. Look, the tears of the oppressed—with no one to comfort them! On the side of their oppressors there was power—with no one to comfort them. And I thought the dead, who have already died, more fortunate than the living, who are still alive; but better than both is the one who has not yet been, and has not seen the evil deeds that are done under the sun. (NRSV 4:1-3)
So I returned, and considered all the oppressions that are done under the sun: and behold the tears of such as were oppressed, and they had no comforter; and on the side of their oppressors there was power; but they had no comforter. Wherefore I praised the dead which are already dead more than the living which are yet alive. Yea, better is he than both they, which hath not yet been, who hath not seen the evil work that is done under the sun. (KJV 4:1-3)
Ecclesiastes thinks that the dead are better off than the living—or, at least, that they're better off than the living people who aren't enjoying life or doing creative work, who are stuck in suffering without anyone to comfort them. He says he thinks it's even better not to have been born at all than to be stuck in this kind of life.
If you see in a province the oppression of the poor and the violation of justice and right, do not be amazed at the matter; for the high official is watched by a higher, and there are yet higher ones over them. (NRSV 5:8)
If thou seest the oppression of the poor, and violent perverting of judgment and justice in a province, marvel not at the matter: for he that is higher than the highest regardeth; and there be higher than they. (KJV 5:8)
The poor suffer because people are always trying to ambitiously defeat each other and get on top of each other. It's a mad rush for power and wealth that can only cause more pain—for the people who are caught up in the rush, too.
Sweet is the sleep of laborers, whether they eat little or much; but the surfeit of the rich will not let them sleep. There is a grievous ill that I have seen under the sun: riches were kept by their owners to their hurt, and those riches were lost in a bad venture; though they are parents of children, they have nothing in their hands. (NRSV 5:12-14)
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. There is a sore evil which I have seen under the sun, namely, riches kept for the owners thereof to their hurt. But those riches perish by evil travail: and he begetteth a son, and there is nothing in his hand. (KJV 5:12-14)
People think that it's good to be rich, and that it'll all be smooth sailing once you've clawed your way to the top. Not so, says Ecclesiastes. The fact that the rich have so much makes them worry more. Also, there's no relying on riches—they might all disappear or just cause more problems.
There is an evil that I have seen under the sun, and it lies heavy upon humankind: those to whom God gives wealth, possessions, and honor, so that they lack nothing of all that they desire, yet God does not enable them to enjoy these things, but a stranger enjoys them. This is vanity; it is a grievous ill. A man may beget a hundred children, and live many years; but however many are the days of his years, if he does not enjoy life's good things, or has no burial, I say that a stillborn child is better off than he. (NRSV 6:1-3)
There is an evil which I have seen under the sun, and it is common among men: A man to whom God hath given riches, wealth, and honour, so that he wanteth nothing for his soul of all that he desireth, yet God giveth him not power to eat thereof, but a stranger eateth it: this is vanity, and it is an evil disease. If a man beget an hundred children, and live many years, so that the days of his years be many, and his soul be not filled with good, and also that he have no burial; I say, that an untimely birth is better than he. (KJV 6:1-3)
This runs along the same lines as the last quote: the rich or fortunate aren't always so rich or so fortunate. It can all turn on a dime. It's better not to have been born than to have only had good things or a lot of things, without ever enjoying them and living in the present.
There is a vanity that takes place on earth, that there are righteous people who are treated according to the conduct of the wicked, and there are wicked people who are treated according to the conduct of the righteous. I said that this also is vanity. (NRSV 8:14)
There is a vanity which is done upon the earth; that there be just men, unto whom it happeneth according to the work of the wicked; again, there be wicked men, to whom it happeneth according to the work of the righteous: I said that this also is vanity. (KJV 8:14)
Here, Ecclesiastes questions the whole idea of justice. Although he'll also say that God will judge everyone—or progresses towards that idea—here, he seems to think it's all a crapshoot. Bad deeds might go unpunished, or actually be rewarded. And the opposite might be true for good deeds committed by good people.
Whoever digs a pit will fall into it; and whoever breaks through a wall will be bitten by a snake. Whoever quarries stones will be hurt by them; and whoever splits logs will be endangered by them. If the iron is blunt, and one does not whet the edge, then more strength must be exerted; but wisdom helps one to succeed. If the snake bites before it is charmed, there is no advantage in a charmer. (NRSV 10:8-11)
He that diggeth a pit shall fall into it; and whoso breaketh an hedge, a serpent shall bite him. Whoso removeth stones shall be hurt therewith; and he that cleaveth wood shall be endangered thereby. If the iron be blunt, and he do not whet the edge, then must he put to more strength: but wisdom is profitable to direct. Surely the serpent will bite without enchantment; and a babbler is no better. (KJV 10:8-11)
This is pretty strong stuff. Any activity you do will injure or kill you if you're not prepared—or if you're not totally present or aware of it. Wisdom is something that can help you avoid the lack of preparation and awareness that could otherwise easily kill you.