The Washington Post has a fascinating article on Iraq and the psychology of entrapment (via Talking Points Memo):
When you invest yourself in something, it is exceedingly difficult to discard your investment. What is devilish about entrapment is not just that it can result in ever greater losses, but that those losses get you ever more entrapped, because now you have even more invested.
[Wesleyan University psychologist Scott] Plous, a social psychologist and author of "The Psychology of Judgment and Decision Making," said experiments show that psychological entrapment comes in at least four guises: the investment trap, in which we try to recover sunk costs by throwing good money after bad; the time delay trap, in which a short-term benefit carries the seed of long-term problems; the deterioration trap, in which things that started out well slowly get worse; and the ignorance trap, in which hidden risks surface suddenly.