Why should a sinner suffer forever in hell fire? In my little knowledge I believe any form of punishment is a way of curbing crimes or wrong doings and for others to learn not to do wrong. When this life ends some would be in heaven and the rest in hell fire as punishment for their wrong doings. 

My question is why should there be punishment forever since there is no one to learn from these people any more and they cannot even repent? Why not just annihilate them and be remembered no more? 

What am I missing? Is my understanding of punishment different? How does Christian doctrine approach the issue of the duration of hell? What purpose do they see it serving that makes it an eternal necessity? What basis do they cite for their understanding?
I immediately thought of C.S. Lewis' "The Great Divorce" upon reading this question. In the book, he puts forth the idea that separation from God is what sinners desire, and God gives them what they desire. I did some digging and found this blog (written by Bird) on the topic: 

"The idea of Hell being something of a choice for the damned fits hand-in-glove with the idea represented by C. S. Lewis who said that the damned souls are in some sense successful rebels to the end, and, as Lewis' character George MacDonald says in The Great Divorce, 


  "There are two types of people in the world. Those who say to God,
  'Thy will be done,' and those to whom God says, in the end, 'Thy will
  be done.'"


I'll end with another Keller quotation from...(The Reason For God): 


  "All God does in the end with people is give them what they most want,
  including freedom from himself. What could be more fair than that?"


Source: "Hope all things about your brethren"