The Buy-In Effect: When Increasing Initial Effort Encourages Follow-Through

Behavioral interventions often focus on reducing friction to encourage behavior change. In contrast, we provide evidence that adding initial friction to a sign-up process can increase follow-through behavior. In a field experiment with a state department of transportation (N = 27,227), we test whether adding modest friction during sign-up for a carpool platform increases usage. While a more effortful sign-up process leads to 25% fewer sign-ups, overall usage increases. Importantly, these results were only partly explained by selection: using an intent-to-treat analysis, participants with a more effortful sign-up process took 1.6 times more carpool trips per week over four months, leading to more overall trips despite fewer users. In a second experiment with online task work, participants with more effortful sign-up were 37% more likely to return the next day and completed more work overall. These results suggest that adding friction may be an overlooked strategy when follow-through, rather than initial uptake, is the primary goal.