Impossibility is an excuse for the nonperformance of duties under a contract, based on a change in circumstances (or the discovery of preexisting circumstances), the nonoccurrence of which was an underlying assumption of the contract, that makes performance of the contract literally impossible. For such a defense to be raised, performance must not merely be difficult or unexpectedly costly for one party; there must be no way for it to actually be accomplished. For example, if Rachel contracts to pay Joey $1000 to paint her house on October 1, but the house burns to the ground before the end of September, Rachel is excused from her duty to pay Joey the $1000, and he is excused from his duty to paint her house; however, Joey may still be able to sue for the unjust enrichment of any benefit conferred on Rachel before her house burned down (e.g.