What it means
Behavioural economists describe this pattern as escalation of commitment. A project begins well and then hits trouble, and each time a manager is asked for a little more money to rescue it, the request seems small compared with what has already been spent.
Over several rounds, the total can grow far beyond the original budget. The trap is dangerous because it feels like prudence.
Leaders say they cannot stop now because they have come too far, which sounds responsible but quietly ties the next decision to the past. The money already spent is gone, so the only fair question is whether the next dollar earns more than it costs.
It appears across industries: failed technology rollouts, construction overruns, marketing campaigns, acquisitions that never integrate. In each case the early spending acts like an anchor, and teams find it harder to see that the plan is no longer working.
Personal reputation and public commitments tend to make the grip tighter, especially when a leader has announced the project to staff, customers or investors. Finance teams can counter the trap with discipline.
They can set a budget cap for each stage, require a fresh business case at every funding request, and keep a record of the assumptions that were made at the start. Comparing the original forecast with the current one often shows how far reality has drifted.
The nuance is that persistence is not always a mistake. Some projects are worth finishing because the remaining spend is small compared with the remaining benefit.
The trap is specifically about letting the past decide, not about continuing when the future numbers genuinely support it.
In practice
Real-world examples.
Example
A construction company is building a hotel that is running 30% over budget. The board approves further funding three times because the project is nearly done, even though the revised forecast shows the hotel will never earn back the extra cost.
Example
A logistics firm keeps patching an old warehouse management system at a cost of $40,000 a quarter. Replacing it would cost $150,000, but managers refuse to switch because of the $1.2 million already invested. Over three years the patching costs alone would exceed the price of the replacement, which nobody has put on the table.
Example
A retailer continues advertising a product that sells poorly because it spent $200,000 on the launch. The marketing director insists that stopping would waste the original spend, and the losses continue each month. By the time a new manager reviews the figures, the campaign has quietly cost far more than the product has earned.
Formula
Calculation
Value of the next funding round = expected future benefit - additional cost (past spending excluded)
Suppose a company has spent $500,000 on a customer platform. It now asks for another $120,000 to finish, and the platform is expected to generate $90,000 of benefit. The value of this round is 90,000 - 120,000 = -$30,000, so the company should stop. The trap reasoning would compare the $120,000 request with the $500,000 already spent and conclude that it is only 24% extra (120,000 / 500,000 = 0.24), which sounds small. That comparison is irrelevant, because the $500,000 is lost whether the company continues or not.Case study
Seen in the real world.
Summit Rail Services is an illustrative, fictional maintenance contractor that began a $2 million upgrade of its scheduling software. After the first year, the project was late and had cost $1.8 million, and the vendor asked for a further $600,000.
The operations director argued that stopping would waste the $1.8 million. The finance director asked the team to list only future numbers, and the revised case showed $450,000 of expected annual savings but substantial risk of further delay.
With a realistic three-year view, the benefits of $1.35 million still exceeded the extra cost of $600,000, so the project passed the test. In this illustrative case, the company continued, but only after a fresh business case, a fixed price and clear stop criteria, which is different from continuing out of habit.
Watch out
Common mistakes.
- Justifying more funding by pointing to the amount already spent, when only future costs and benefits should count.
- Believing that the trap only affects careless people, when experienced professionals fall into it as well.
- Treating every decision to continue as a trap, when continuing can be right if future benefits exceed future costs.
Questions
People also ask.
How is the sunk cost trap different from the sunk cost dilemma?
The trap is the repeated pattern of over-investing, while the dilemma is the single moment of choice between stopping and continuing.
What simple control reduces the risk?
Setting a stage budget and a stop rule at the start, and requiring a new business case for every extra funding request, makes it harder to drift.
Can small businesses fall into it too?
Yes, a small business owner with personal savings in a failing venture may be even more reluctant to stop, so an outside adviser can help.
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