What is the Sunk Cost Fallacy?

Definition

You've invested £3M in a technology platform. It's not working. Market feedback is poor. Internal adoption is failing. But you've committed £3M (abandoning now feels like admitting failure. So you invest another £2M. Then £1M more. Eighteen months and £6M later, you finally shut it down. The last £3M was spent defending the first £3M. All six million are now worthless.

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This is the sunk cost fallacy.

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The sunk cost fallacy is the tendency to continue investing in a project, strategy, or course of action because of previously invested resources (money, time, effort)) even when continuing no longer makes economic sense based on future value. It's the error of letting past costs influence future decisions when those costs are irrecoverable and therefore irrelevant to forward-looking analysis.

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The fallacy is powerful because abandoning sunk costs feels like waste. "We've already spent £3M we can't let that go to waste." But the £3M is already wasted whether you stop now or spend £3M more. The only question is: does future investment create future value? Past investment is irrelevant.

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Why the Sunk Cost Fallacy Destroys Value

The sunk cost fallacy creates systematic value destruction:

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Escalates commitment to failing strategies: The more you've invested, the harder it becomes to stop even as evidence of failure accumulates. Property developers complete buildings they know won't lease profitably "because we've already invested £20M in site acquisition and planning." The £20M is gone. Continuing construction destroys another £30M.

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Prevents reallocation to better opportunities: Every pound spent defending sunk costs is a pound not invested in opportunities with positive expected returns. The consultancy that keeps underperforming partners "because we've invested years developing them" is choosing to not invest in recruiting high performers. The opportunity cost compounds.

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Signals loss of strategic discipline: When organisations systematically throw good money after bad, investors and talented employees notice. "They can't kill failing projects" becomes the reputation. This attracts capital and talent that values decisiveness elsewhere.

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Creates organisational learned helplessness: Teams learn that struggling initiatives don't get killed, they get more resources. This incentivises gaming: if I can get initial approval and spend quickly, the project becomes unkillable. Strategic discipline disappears.

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Practical Application

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Immediate technique: For any struggling initiative, ask: "If we hadn't already invested anything, would we choose to invest what we're about to invest now, based solely on expected future returns?" If the answer is no, stop. The past investment is irrelevant. Only future value-creation matters. This reframing bypasses the sunk cost trap.

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Common mistake to avoid: Conflating sunk cost discipline with short-termism. "If we applied your logic, we'd never invest in anything long-term." False. Long-term investments should be continued when future expected returns justify future investment. Killing failing projects isn't short-termism it's capital discipline. The difference is: are you defending past decisions or funding future value?

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Want to develop systematic approaches to capital allocation that prioritise future value over past investment?Take the Composure Audit to understand your decision patterns. Or to build disciplined decision-making capability for your organisation, book a 15-minute discovery call.