McCain invokes sunk cost thinking in 1st Presidential debate

As I write this, I'm watching a rerun of the first presidential debate between John McCain and Barack Obama. They have just got onto the topic of Iraq and Afghanistan. I was struck by something that McCain said. He described meeting the mother of a US soldier who had died in Iraq. The woman expressed her support for McCain, gave him a wristband and asked that he ensure that her son had not died in vain. In the debate, McCain went on to say that he would honour this woman's wish and never allow defeat to occur in Iraq, or to withdraw troops before establishing security.

I'm not making any argument here about the US and allied presence in Iraq, but I simply note that John McCain's reasoning commits a basic fallacy of decision making. From a rational point of view, the decisions we make should be guided by a consideration of the likely outcomes of our decisions; that is, what costs and benefits are likely to follow? What's not rational is to base our decisions on investments that we have made in the past.

Research conducted by psychologists shows, however, that sunk cost thinking is widespread (http://en.wikipedia.org/wiki/Sunk_cost) . For example, in a classic study conducted by Arkes and Blumer (1985) students who purchased season tickets for the campus theatre were randomly allocated either full price tickets or discounted tickets. During the first half of the semester students who had paid full price attended the theatre more often (presumably feeling they had to get their 'money's worth'). Other examples abound, some of which show that people are more likely to continue trying to redeem a failing course of action where some previous investment has been made.

In the case of war, decisions should be made on an assessment of likely future outcomes. Continuing a war in order to ensure that others didn't die in vain may well be ensuring the future deaths of other soldiers (and, indeed, civilians).