When you place this verse in the context of the chapter, you see the first nine verses are the well-known and sung lyrics about there being a time for everything under the sun. Then, verse ten says that Solomon has taken a look at the work, or jobs that mankind does, their occupations. He has had a look around at the different jobs with which men fill their time. Then in verse twelve, he decides that the only thing good about work, is to make yourself and family happy and do good deeds for others (with your income.) Sandwiched right there in the middle of these two verses after the lyrics about time, is verse eleven reminding us of eternity and God's work. The King James uses the word world, while the NKJV uses eternity. The Hebrew gives you the idea that it is talking about the daily grind that never ends in this world...infernal, the dog-eat-dogness of life.
This makes it clear that God put the tedium in our days. We are so busy figuring out the day-to-day of life, that we will never solve the matters of the universe. As and example, look at the government space program, NASA. We can't afford the shuttles now. Industry will have a crack at it, because the government can't afford to host it anymore. Day-to-day matters of survival always impede advancement on a grand scale. The Roman Empire rose and fell. The British Empire rose and fell. Kingdoms come and go. One thing remains...God never changes.