When parties to a contract make promises to perform their obligations, and one party reasonably relies on the other party’s promise—but the party making the promise fails to perform, causing harm or loss to the party who relied on the promise—the party who relied on the promise to perform is said to have relied to its detriment.

This legal concept is called detrimental reliance. Detrimental reliance may serve as a substitute for consideration, and make an otherwise unenforceable contract enforceable.

Thus, detrimental reliance is a legal concept based on fairness (known as equity or equitable), and is equivalent to contractual promissory estoppel (due to the other party’s reliance, the party who did not keep its promise is prohibited from challenging the enforceability of its promise).

Detrimental reliance is not a separate tort cause of action.

In Hawaii, the legal concept of detrimental reliance, also known as promissory estoppel, is recognized and can be used to enforce a contract that may otherwise lack consideration and be unenforceable. This doctrine applies when one party makes a promise that the other party relies upon, and as a result of this reliance, the latter party suffers a loss or harm when the promise is not fulfilled. The reliance must be reasonable, and the resulting detriment must be substantial. In such cases, the party who made the promise may be estopped from denying the enforceability of the promise, based on the principles of fairness and equity. Detrimental reliance is not considered a separate tort but rather a principle that can affect the enforceability of contractual promises. Hawaii state statutes and case law would provide specific applications and limitations of this doctrine.