In proprietary estoppel claims arising from informal family arrangements, the reasonableness of the plaintiff's assumption must be assessed in the full context of the parties' relationship and conduct over time, not by reference to a single conversation or document in isolation. The plaintiff's understanding need not fit into conventional legal categories (lease, licence, loan), and the expectation need not be sufficiently certain to amount to a valid contract. Loss of the chance to acquire an alternative property is sufficient detriment provided it is not fanciful or unrealistic; the plaintiff need not prove on the balance of probabilities that they could have purchased an alternative home.
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