What Is a Sunk Cost? How to Avoid the Sunk Cost Fallacy in Product Decisions
A sunk cost is any investment — of money, time, effort, or resources — that has already been made and cannot be recovered. In business, sunk costs include expenses already incurred on marketing, research, software development, equipment, salaries, and facilities. The defining characteristic is irreversibility: the money is spent and cannot be reclaimed regardless of future decisions.
The concept is fundamental in decision theory and economics, and it’s especially relevant for product managers who are constantly deciding whether to continue, pivot, or stop investing in initiatives.
The Sunk Cost Fallacy
The sunk cost fallacy is the cognitive bias that causes people to continue investing in something because of past investment, even when the rational decision would be to stop. The logic goes: “We’ve already spent so much on this — we can’t stop now.”
This reasoning is flawed because past expenditures are irrelevant to future value. The only question that matters when deciding whether to continue is: Does continuing this effort create more value than alternative uses of the same resources going forward?
What’s been spent doesn’t change the answer to that question. It’s gone either way.
Why the Sunk Cost Fallacy Is So Common
Sunk cost thinking is deeply human. Several psychological forces reinforce it:
- Loss aversion — We feel the pain of losses more acutely than the pleasure of equivalent gains, making it psychologically difficult to “accept” a loss by abandoning an investment
- Commitment and consistency — Once people commit to a course of action, they’re motivated to remain consistent with that commitment
- Escalation of commitment — Each additional investment makes abandonment more emotionally difficult, even as the returns diminish
- Identity attachment — When people are personally identified with a project or decision, abandoning it feels like admitting failure or admitting they were wrong
Sunk Costs in Product Management
Product managers encounter sunk cost pressure constantly:
- Feature development that isn’t working: “We’ve spent three sprints on this feature — we have to ship it.”
- Products past their prime: “We’ve invested millions in this product line — we can’t sunset it.”
- Strategic initiatives with poor outcomes: “The CEO approved this strategy last year — we can’t admit it’s not working.”
In each case, the sunk cost is real — but it’s irrelevant to the decision. The decision should be based entirely on the expected future value of continuing versus redirecting resources.
How to Avoid Sunk Cost Thinking
Make Investment Decisions at Defined Milestones
Rather than reviewing projects continuously, set explicit decision points where the team evaluates whether to continue, pivot, or stop based on evidence and forward-looking value — not on what’s already been spent.
Separate the Decision from the History
When evaluating whether to continue an investment, explicitly ask: “If we hadn’t already spent anything on this, would we start today with what we know?” If the answer is no, that’s important signal.
Frame Decisions in Terms of Opportunity Cost
Continuing to invest in something always has an opportunity cost — the value of what else those resources could be used for. Making the opportunity cost explicit shifts the frame from “we can’t stop” to “what’s the best use of our resources going forward?”
Create Psychological Safety for Changing Course
In organizational cultures where changing direction is interpreted as admitting failure, sunk cost pressure increases. Leaders who model and celebrate course corrections based on new evidence create environments where better decisions can be made.
Distinguish Sunk Costs from Abandonment
There’s sometimes real value embedded in a struggling initiative — IP developed, customer relationships built, technology created. A decision to stop investing doesn’t have to mean abandoning all of that; some assets can be repurposed or redirected.
Key Takeaways
The sunk cost fallacy is one of the most expensive cognitive biases in business. Product teams that learn to recognize it and make forward-looking decisions based on expected future value — rather than justifying past investments — are more agile, more rational, and significantly better at allocating resources to where they’ll actually matter.