Promises and expectations.

We investigate why people keep their promises in the absence of external enforcement mechanisms and reputational effects. In a controlled laboratory experiment we show that exogenous variation of second-order expectations (promisors' expectations about promisees' expectations) leads to a significant change in promisor behavior. We provide evidence that a promisor's aversion to disappointing a promisee's expectation leads her to behave more generously. We propose and estimate a simple model of conditional guilt aversion that is supported by our results and nests the findings of previous contributions as special cases. [ABSTRACT FROM AUTHOR]