我觉得这算part of equity law “ the doctrine of Promissory Estoppel'. 简单来说就是因为对方的某些行为对你的一些行为照成了影响,给你带来了损失. 因为你act upon the other party's actions, the first party has played some role in the creation of the second party's assumption or expectation and you would suffer material detriment.