Ecclesiastes 2:20-23

Therefore I completely despaired of all the fruit of my labor for which I had labored under the sun. When there is a man who has labored with wisdom, knowledge and skill, then he gives his legacy to one who has not labored with them. This too is vanity and a great evil. For what does a man get in all his labor and in his striving with which he labors under the sun? Because all his days his task is painful and grievous; even at night his mind does not rest. This too is vanity.