Glossary · Behavioral Economics
Sunk Cost Fallacy
Definition
The sunk cost fallacy is the tendency to continue investing in a project, product, or relationship because of cumulative prior investment, regardless of whether additional investment produces positive expected value. In product adoption, it creates both productive lock-in (customization investment) and destructive persistence (continuing to use a failing tool).
Rational decision theory says only future costs and benefits should influence choices — past investment is irrecoverable. Yet humans consistently let prior investment drive forward decisions. This creates the 'too-much-to-quit' dynamic in product adoption: a customer with extensive customization continues using a worse tool because of psychological investment, even when switching has positive expected value.
Essays on this concept
- Behavioral Economics
Sunk Cost Fallacy in Product Adoption: Why Users Who Customize Retain 4x Longer
Economists call it irrational. Product managers call it retention. The sunk cost fallacy — when properly channeled through customization and effort investment — becomes the most reliable predictor of long-term user engagement.
- Behavioral Economics
Sunk Cost Fallacy in Product Adoption: Why Users Who Customize Retain 4x Longer
Economists call it irrational. Product managers call it retention. The sunk cost fallacy — when properly channeled through customization and effort investment — becomes the most reliable predictor of long-term user engagement.
- Behavioral Economics
The Endowment Effect in SaaS Pricing: Why Free Trials Convert Better Than Freemium
A behavioral economics analysis of why giving users temporary full access converts 2-5x better than permanent limited access. We examine the endowment effect, the IKEA effect, sunk cost psychology, and present an original framework for SaaS pricing architecture.
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