In contract law, the doctrine of consideration states that there must be an exchange of consideration in order for a contract to be enforced. If one party fails to uphold their end of a contract, the other party can withdraw from that contract. Promissory estoppel is the exception to this rule. Under the doctrine of promissory estoppel, even the existence of a promise may be sufficient to enforce an agreement, if the other party has suffered damage as a result of acting on that promise.