Proverbs is a young, smart, idealistic teacher who tells us that God weaves the universe together through wisdom. There is a pattern of justice.
Ecclesiastes is the middle-aged cynic. He tried Proverbs’ way, and it doesn’t always work.
Job is a wise, weathered old man who has learned, through life’s ups and downs, that God’s wisdom is deeper than we can possibly understand. We simply trust in the ultimate goodness and faithfulness of God.