Ch4. The Sunk Cost Fallacy and Regret Aversion — Why We Keep Making Bad Choices

“We’ve Come This Far…”

Sitting through a boring movie because you already paid for the ticket. Finishing a bad meal at a buffet because it cost $40. Staying in an incompatible relationship because you’ve been together for two years. Continuing a failing project because you’ve already invested three years in it.

What do all of these share?

Past costs are driving present bad decisions.

Economists call this the Sunk Cost Fallacy.

What Is a Sunk Cost?

A sunk cost is a cost that has already been incurred and cannot be recovered.

The principle of rational economics is clear: sunk costs should have no bearing on future decisions. The past expenditure has happened; future decisions should consider only future costs and benefits.

Example:

You paid $15 for a movie ticket. Thirty minutes in, you’re bored and the film is clearly getting worse.
Rational analysis: if the remaining movie is not worth your remaining time, leave.
Actual behavior: “I already paid, so I’ll stay.”

The $15 is gone whether you stay or go. The only cost of remaining is the rest of your evening.

Psychological Roots of the Sunk Cost Fallacy

1. Loss Aversion

From Prospect Theory (Chapter 1): losses feel approximately 2.25 times as painful as equivalent gains feel pleasurable.

Acknowledging a sunk cost means confirming a loss. “I made a bad choice” is painful to admit. By continuing to invest, we maintain the psychological fiction that the loss is not yet finalized.

2. Consistency Desire

People want to see themselves as consistent. “I invested in this” → “therefore it must be valuable” → “therefore I should continue” — this logic chain runs automatically, even when the opposite is true.

3. Completion Bias

The discomfort of leaving something unfinished. The brain tends to dwell on incomplete tasks (the Zeigarnik Effect). This discomfort pushes people to complete things even when completing them is irrational.

The Sunk Cost Fallacy in Practice

In Investing

“I’m already down 50% — if I sell now, I lock in the loss.” → The investor watches the position fall further, compounding the damage.

Warren Buffett: “When you find yourself in a hole, the best course of action is to stop digging.”

In Relationships

“We’ve been together for five years” becomes the reason to continue an incompatible relationship. But those five years are already spent. The only real question is how to spend the next five.

In Business and Projects

Companies continue pouring budget into failed projects because the amount already spent creates enormous psychological pressure to persist. The Concorde Fallacy (Concorde Effect) is named for exactly this: the British and French governments discovered early in development that the supersonic jet would never be commercially viable — but the billions already invested made stopping feel impossible. They spent decades continuing what they knew was a mistake.

Regret Aversion

Closely intertwined with the sunk cost fallacy is Regret Aversion.

People fear regret more intensely than simple loss. “My decision caused this outcome” creates far more pain than the same outcome attributed to external forces.

Action Regret vs. Inaction Regret

In the short term: regret from action (“I shouldn’t have done that”) is more intense. In the long term: regret from inaction (“I should have tried”) is stronger and more persistent.

Research by Gilovich and Medvec (1994) found that what older people regret most are the things they didn’t do — dreams not pursued, feelings not expressed, projects never started.

This asymmetry has an important implication: tolerating short-term discomfort to act is the better strategy for minimizing long-term regret.

Regret Aversion and Status Quo Bias

“If I change course and it goes wrong, I’ll regret it more than if I do nothing and it goes wrong.” This fear of action-induced regret keeps people stuck with the status quo — ignoring the fact that inaction regret grows larger over time.

Strategies for Better Decisions

1. Zero-Based Thinking

“If I were making this decision fresh today, with no prior commitments, would I make the same choice?”

Mentally set the past to zero. Evaluate the situation purely on current information and future prospects. “Would I start this relationship today?” “Would I begin this project today?“

2. Ask Your Future Self

“How will I see this decision one year from now?” Shift perspective from the immediate pain of the loss to a longer time horizon.

3. Reframe: Loss Frame vs. Gain Frame

“If I quit, I lose what I’ve already put in.” → Loss frame “If I quit, I reclaim the time and energy I’d otherwise spend.” → Gain frame

Viewing the same situation through a gain frame produces more rational decisions.

4. Pre-commitment (Exit Rules)

Before starting an investment or project, define in advance: “Under what conditions, and at what threshold, will I stop?” Setting a stop-loss level, a project review date, or a relationship re-evaluation point before emotions are engaged reduces vulnerability to the sunk cost trap when things go wrong.

Chapter Summary

Concept	Description	Real-Life Example
Sunk Cost	Irrecoverable past expenditure	Money already spent on a ticket
Sunk Cost Fallacy	Past costs distorting future decisions	Sitting through a bad movie
Concorde Effect	Continuing a failing project	Escalating budget on a failing product
Regret Aversion	Avoiding regret by maintaining status quo	Choosing inaction to avoid blame
Inaction Regret	Long-term regret grows larger over time	Regretting dreams not pursued

Countermeasures:

Zero-based thinking (“If starting fresh, would I still choose this?”)
Ask your future self
Reframe in gains, not losses
Pre-commitment with defined exit rules

Next chapter: The Availability Heuristic and Representativeness Bias — why the things that come to mind most easily feel most true.

OIYO Editorial