Proprietary estoppel is a reliance or expectation created or encouraged by a property owner towards another to alter his or her position to their detriment in the expectation of obtaining a proprietary interest: Handley JA in Delaforce v Simpson-Cook [2010] NSWCA 84 at 21. An example would be a promise of property upon death by one person to another (i.e. husband to wife) on the performance of certain duties or the forfeiture of a debt.