Sunk Cost Fallacy

People irrationally continue investing in something because of what they've already spent, not what they'll gain.

stellae.design

Cognitive

The Sunk Cost Fallacy has been studied extensively in behavioral economics by researchers including Hal Arkes and Catherine Blumer (1985). It describes the tendency to continue investing in a losing proposition because of what has already been spent, even though rational decision-making should only consider future costs and benefits. The fallacy is driven by loss aversion (not wanting to 'waste' past investment) and commitment bias. In digital products, this plays out in subscription retention, feature investment, and user loyalty.

Why It Matters

The sunk cost fallacy is the tendency to continue investing in something because of previously invested resources, rather than evaluating future value objectively. In product design, it manifests as users persisting with a frustrating process because they have already spent time on it, or teams refusing to abandon a failing feature because of development effort already spent. Recognizing this bias helps designers build experiences that respect user time and helps teams make better product decisions.

Real-World Examples

Draft auto-save in a long form

A job application form auto-saves after every field, allowing candidates to close the browser and return days later without losing work. This removes the sunk cost pressure of feeling forced to complete a 45-minute application in one sitting. Candidates can make better decisions about whether to continue because leaving is not punished.

Progress-preserving cancel in onboarding

A SaaS onboarding wizard lets users skip steps and return to them later, preserving everything already completed. Users see a dashboard showing which steps are done and which remain, reframing the experience as flexible rather than all-or-nothing. This reduces the anxiety of commitment and increases completion rates.

Counter-example

Non-refundable time investment trapping users

A subscription cancellation flow requires users to navigate through 7 screens of retention offers after they have already decided to leave. Users who invested 10 minutes reaching the cancel button feel compelled to finish, but each additional screen adds friction designed to exploit sunk cost thinking. This dark pattern damages trust and generates negative word-of-mouth.

Role-Specific Guidance

Common Mistakes

• Teams often fall into sunk cost thinking themselves, continuing to invest in features with poor adoption because 'we already built it' rather than cutting losses and redirecting effort. Designers sometimes exploit sunk cost psychology as a retention mechanism — making cancellation painful because users 'already invested' — which is a dark pattern that erodes trust. Confusing sunk cost framing with genuine progress indicators is another error: showing '80% complete' to pressure users forward is manipulative if the remaining 20% is disproportionately difficult.