'Vain' in the Bible

I have seen that every [effort in] labor and every skill in work comes from man’s rivalry with his neighbor. This too is vanity (futility, false pride) and chasing after the wind.

One hand full of rest and patience is better than two fists full of labor and chasing after the wind.

And I have turned, and I see a vain thing under the sun:

For who knoweth what is good for man in this life, all the days of his vain life which he spendeth as a shadow? for who can tell a man what shall be after him under the sun?

I have seen all these things in my vain life: Sometimes a righteous man perishes in [spite of] his righteousness, and sometimes a wicked man lives a long life in [spite of] his evil.

Live joyfully with the wife whom you love all the days of your fleeting life which He has given you under the sun—all the days of vanity and futility. For this is your reward in life and in your work in which you have labored under the sun.