Ecclesiastes 2:20-23

Therefore I turned about to cause my heart to despair concerning all the labor wherein I had labored under the sun. For there is a man whose labor is with wisdom, and with knowledge, and with skilfulness; yet to a man that hath not labored therein shall he leave it for his portion. This also is vanity and a great evil. For what hath a man of all his labor, and of the striving of his heart, wherein he laboreth under the sun? For all his days are but sorrows, and his travail is grief; yea, even in the night his heart taketh no rest. This also is vanity.