Repeating about two or three different points, Ecclesiastes goes on. He says that a man might not have a chance to enjoy the wealth he's earned, and someone else will end up getting it. It's horrible. It's vanity.
If a person has a hundred kids, life still might be a bust if he never enjoyed the good things. It would be better to be a still-born child—even though he or she never sees the light of day, at least they got a long rest. It's better to just chill out in the womb, than toil "under the sun." Everyone's going back to the dust anyway, and what's a life of a thousand years compared to an eternity of silence? It's barely anything.
Take a Picture—It'll Last Longer
The Preacher keeps preachin'. He tells us that we keep trying to fulfill our appetites, but it's a futile game. Our desires can't be quenched.
This leads him to the conclusion that "the seeing of the eye is better than the wandering of the desire" (6:9). It's better to pleasantly observe life and take it all in, than to keep trying to scratch an itch that can never be scratched.
And talking too much doesn't help, either. Ecclesiastes attacks using a lot of words as—you guessed it—vanity. You need to just let life happen, realizing that your knowledge of the world will always be too limited to see what's really, ultimately good for everyone.