Sophistry
No. 18 Cognitive bias

Sunk Cost Fallacy

Keep going with something because of what you've already invested, not because it's still worth it.

A cost bar cut by a vertical line marking today, with a shorter bar of value below it. a b c d
FIG. 18a, already spent. b, what continuing costs from here. c, what finishing is worth. d, a carried across into the decision.

Illustrative example

"We've already spent £40,000 on this software, we can't stop now," even though finishing costs another £60,000 for something nobody actually wants.

Money, time, or effort already spent is gone regardless of what happens next. The sunk cost fallacy weighs that past spending as if it were still a reason to keep going, rather than looking only at the cost and benefit of continuing from today.

A rational decision only cares about future costs and future benefits. The £40,000 already spent doesn’t change whether the remaining £60,000 is worth spending.

Ask: “if I hadn’t spent anything yet, would I start this today?” If the answer is no, the past spending isn’t a reason to continue.

Seen in the wild

Real, sourced instances of this technique in actual public debate.

Examples are chosen for how clearly they show the technique, not for who said it.

George W. Bush

Leans right

President of the United States

“These brave men and women gave their lives for a cause that is just and necessary for the security of our country, and now we will honor their sacrifice by completing their mission.”

August 24, 2005 (remarks to military families, Nampa, Idaho)Official White House transcript archive of the remarks (opens on the source site)

Context
Speaking to military families and the Idaho National Guard during a period of falling public support for the Iraq war and growing pressure for a withdrawal timetable.
Reading
Whether to continue depends on what continuing will cost and achieve from here. The lives already lost cannot be recovered by any future decision, so they cannot count as a reason either way. The argument nonetheless treats them as the reason, which is what makes withdrawal feel like a betrayal rather than a calculation. This is the hardest version of the fallacy to name out loud, because saying so sounds like calling the sacrifice worthless, and it is not.

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