Zero out past investment before evaluating the forward decision
Explicitly set prior investment to zero and evaluate only what each future path offers from here.
Why it works
The sunk cost fallacy works by making past investment emotionally salient at the moment of forward decision. Deliberately zeroing it out in the analysis creates a clean forward-only frame. The prior investment is neither added to nor subtracted from the value of future paths — it simply does not appear in the calculation, because it cannot affect outcomes.
How to do it
- Before any continuation decision, write the past investment (time, money, effort) in a column labeled "irrelevant."
- Now list only: what will happen if I continue? What will happen if I stop?
- Evaluate only those forward outcomes against each other.
- Make the decision that produces the better forward outcome, regardless of what is in the "irrelevant" column.
Evidence
Arkes and Blumer (1985) demonstrated in controlled experiments that prior investment systematically increases willingness to continue bad courses. Zeroing-out framing is the standard economic and decision-theoretic antidote. Ronayne, Sgroi, and Tuckwell (2021) stress-tested the effect across a large incentivized experiment, confirming it is real but more bounded than early demonstrations implied. (rct)
Knowing about the fallacy reduces but does not eliminate it; the emotional salience of past investment is difficult to fully override even with correct analysis.
Sources
- Arkes & Blumer (1985), the psychology of sunk cost, Organizational Behavior and Human Decision Processes
- Arkes, H. R., & Blumer, C. (1985). The psychology of sunk cost. Organizational Behavior and Human Decision Processes, 35(1), 124-140.
- Ronayne, D., Sgroi, D., & Tuckwell, A. (2021). Evaluating the sunk cost effect. Journal of Economic Behavior & Organization, 186, 318-327.
Common mistake
Writing down the past investment and then trying to "ignore" it mentally — it remains visible and continues to influence judgment. Better to physically move it out of the working analysis frame.
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More practices for The Sunk Cost Fallacy: Escaping Bad Investments
- Apply the new investor test
Ask: would a rational person who had not already invested choose to invest now?
- Set stop-loss policies before starting projects
Define exit criteria at the start, when you are not yet sunk.
- Separate your identity from the investment
The fact that you chose this doesn’t mean continuing is who you are.
- Actively watch for escalation of commitment
Each new investment in a losing course makes the next exit harder — catch escalation early.
- Use regret minimization as a forward-looking check
At 80, which will you regret more — stopping now, or having continued into a deeper hole?
- Calculate the ongoing cost of delay
Every day you continue a bad course is a day you could have started a better one.
Related concepts
- Opportunity Cost Thinking: What You Give Up When You Choose
The hidden price of every choice — and the practices that make it visible
- Expected Value Thinking: Deciding Under Uncertainty
The math of rational choice under uncertainty, its real limits, and how to use it anyway
- Thinking, Fast and Slow, Made Usable
Two systems, the biases they create, and when to slow down
- Loss Aversion, Made Practical
Why losses loom larger than gains — and how to reframe the decision