Proprietary Estoppel in a Procrustean Bed

In the first place the plaintiff must have made a mistake as to his legal rights. Secondly, the plaintiff must have expended some money or must have done some act (not necessarily upon the defendant's land) on the faith of his mistaken belief. Thirdly, the defendant, the possessor of the legal right, must know of the existence of his own right which is inconsistent with the right claimed by the plaintiff . . . Fourthly, the defendant, the possessor of the legal right, must know of the plaintiff's mistaken belief of his rights . . . Lastly, the defendant, the possessor of the legal right, must have encouraged the plaintiff in his expenditure of money, or in the other acts which he has done, either directly or by abstaining from asserting his legal right.5