You paid €200 for a concert ticket. The day arrives and you have a migraine, it is raining, and you would genuinely rather stay home. Do you go?
Most people do. The reasoning: I already paid for it.
However, that €200 is gone whether you attend or not. The only rational question is: will going to this concert make my evening better or worse? The past payment is economically irrelevant to that decision. Learn more: Loss Aversion Examples: 7 Real Cases That Cost Investors Money.
This is the sunk cost fallacy — continuing a course of action based on resources already spent that cannot be recovered. In personal finance and investing, it quietly destroys more wealth than most investors realize. Learn more: Confirmation Bias in Investing: Why Bad Positions Stay in Portfolios.
Why Sunk Costs Feel Like Real Constraints
Two psychological mechanisms drive sunk cost errors in financial decision-making.
First, loss aversion — documented by Kahneman and Tversky — makes abandoning a losing investment feel like experiencing the loss fresh, even though the loss already occurred. Holding the position does not prevent the loss; it only delays processing it. However, the brain does not make that distinction cleanly.
Second, identity and consistency add another layer. Committing to an investment is, in a small way, a declaration of judgment. Consequently, reversing it means admitting the original judgment was wrong. For investors who see themselves as rational and analytical, this is often more uncomfortable than the financial cost of persisting.
As a result, investors continue allocating resources to failing positions not because the analysis supports it, but because stopping forces a reckoning with a past decision.
Where the Sunk Cost Fallacy Appears in Portfolios
Averaging down on a failing thesis
“I bought at €50, it is now at €32, so I will add more to lower my average cost.” Averaging down can be a legitimate strategy — but only if the thesis remains intact. However, for many investors the decision is driven primarily by the desire to make the original entry price feel less wrong, not by updated analysis.
Therefore, the relevant question is never how much have I already invested? It is always: given everything I know today, is this the best use of this capital?
Continuing non-viable business commitments
Entrepreneurs are particularly vulnerable to sunk cost thinking. Specifically, having invested two years and €80,000 into a venture, each passing month makes stopping psychologically harder — even when every metric signals the model does not work. The accumulated time and money feel like obligations rather than costs already borne.
In fact, research on business failure consistently finds that many non-viable ventures could have been identified significantly earlier — founders continue based on sunk investment rather than forward-looking analysis.
Staying in financial products that no longer make sense
“I have been paying into this whole-life policy for nine years.” The surrender value may be less than premiums paid, but that shortfall is already realized. However, the relevant question is whether this product makes sense going forward — not whether stopping confirms a past mistake.
Moreover, the same logic applies to subscriptions, club memberships, software tools, and any ongoing commitment where historical investment has become the main justification for continuing.
The Zero-Based Decision Framework
The most effective counter to sunk cost reasoning is zero-based decision making: evaluating every ongoing commitment as if you were considering it fresh today.
The question is simple: If I did not already have this position — would I start it today, with what I know now?
If the answer is no, sunk cost thinking is almost certainly what is keeping you in it. This framework works because it separates the forward-looking decision — which is what matters economically — from the backward-looking emotional accounting that feels significant but is not.
Reframe losses as information costs
Professional investors who handle this well typically reframe closed losses as information costs — the price of learning something about a market, a company, or their own decision process. In fact, every investor who has operated across a full market cycle has made decisions that did not work out. Ultimately, the variable is whether those decisions produce useful learning or just emotional baggage carried into the next one.
Key Takeaways
- Sunk costs are unrecoverable — they are economically irrelevant to all future decisions
- Loss aversion and identity protection are the two main engines behind sunk cost errors
- Averaging down is only rational if the thesis remains intact — not to fix the entry price emotionally
- The zero-based question (would I start this today?) cuts through sunk cost reasoning clearly
- Reframing past losses as information costs removes their psychological weight
Sunk costs are sunk. Therefore, the only capital you can protect is the capital you have not yet committed to the wrong decision.
Further Reading
A note from professional practice: The sunk cost fallacy is particularly costly in real estate investment analysis. Once significant due diligence costs have been spent on a deal — legal fees, technical audits, financial modeling — there is enormous pressure to proceed even when the numbers no longer justify it. “We’ve already spent X on this” is a sunk cost argument. The correct question is always: “If we had spent nothing so far, would we start this deal today?” If the answer is no, the rational decision is to stop.