Ecclesiastes 2:19

2:19 Who knows if he will be a wise man or a fool?

Yet he will be master over all the fruit of my labor

for which I worked so wisely on earth!

This also is futile!

Ecclesiastes 3:21

3:21 Who really knows if the human spirit ascends upward,

and the animal’s spirit descends into the earth?

Ecclesiastes 8:1

Human Government Demonstrates Limitations of Wisdom

8:1 Who is a wise person? Who knows the solution to a problem?

A person’s wisdom brightens his appearance, and softens his harsh countenance.