Promissory liability refers to a legal principle that holds a party accountable for the promises they make, especially when the other party relies on those promises to their detriment. This concept is primarily rooted in promissory estoppel, which prevents a promisor from arguing that an underlying promise should not be legally enforced if the promisee has reasonably relied on it and suffered harm as a result. In essence, it ensures fairness by recognizing that certain promises, even without a formal contract, can create binding obligations.