Promises on the go: A field study on keeping one's word.

Promises are voluntary commitments to perform a future action and are often thought to be powerful levers for behavioral change. Here we studied the effectiveness of promises in two preregistered, incentivized field experiments with German students ( = 406) on the premises of a cafeteria. In Experiment 1, the majority of participants (63%) kept their promise to pay back at least half of a € 4-endowment, even though there was no foreseeable cost of breaking the promise, reputational or otherwise.