"I’m not going pull the troops off the battlefield before the mission is complete."
--President George W. Bush, speech in Riga, Latvia, November 28, 2006
This kind of determination always sounds good, but it fails miserably when the battlefield and mission were poorly chosen in the first place. In the case of Iraq, the original mission (WMDs) was hollow and the new mission (quell insurgency) was thrust upon us. And we did not choose the battlefield: it was Al Qaeda that decided to fight us in Iraq, not the other way around. It was never our plan to fight Al Qaeda there... they weren't even in Iraq before we got there.
I thought I might recall a few other instances where such simplistic stubbornness got us into trouble, or would have done:
The German army breaks itself against Stalingrad, 1942-43
"The Miracle of Dunkirk" 330,000 allied soldiers evacuate France, 1940
ANZAC troops are slaughtered at Gallipoli, 1915