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
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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