The self-destructive tendency to carry on investing in a failing project, idea, or enterprise on the grounds that you have already invested heavily in it. This is a kind of wishful thinking.
For example, if you have bought a television that keeps breaking down and you have paid many hundreds of pounds in having it repaired, you may be tempted to keep fixing it on the grounds that you have already invested this money in it. This is probably irrational. You might, reasonably, on environmental grounds, be concerned about throwing out a television set that could be repaired, but if your reason for keeping it is solely that you have already invested in it by having it repaired again and again, then you are have fallen for the sunk-cost fallacy. Just because you have invested large sums of money in it, it doesn’t follow that the best course of action is to keep channelling funds in this direction. You need therapy that will make you let go of that investment if it is a poor one and realise that, to quote a saying, you are simply ‘throwing good money after bad’ (see truth by adage).
Barry Shwartz, described the current situation in Iraq in these terms in an article in an article in the Los Angeles Times (quoted in The Week, 30 Sept. 2006, pl.15): ‘Politicians from both parties are on the record as saying we must persevere with the conflict because thousands of soldiers would otherwise have sacrificed their lives in vain.’ I suppose what these politicians have omitted to mention is that the cost of persevering won't necessarily be one that makes the previous sacrifices worthwhile: the cost may be that more soldiers will sacrifice their lives in vain. The reason for committing further troops shouldnt be that there is a reasonable chance of a favourable outcome, not that we have already paid a high cost in lives. Of course, Shwartz may be taking this 'argument' more seriously than it deserves to be taken, since it could be political rhetoric rather than a seriously presented piece of reasoning.