The law of frustration is tantalizingly simple when it comes to stating it, but incredibly hard when it comes to applying. One would be getting the wrong end of the stick if one were to treat various judicial statements surrounding the doctrine as axioms to be applied in a rule-like manner. Doing so would wrongly lead to a disproportionately large number of ‘false positives’. The purpose of this article is two-fold. First, it seeks to give heuristic short-cuts to anticipate a common law judge’s approach to a frustration case which is poorly captured in definitions and formulae. It seeks to do so by focussing on the ‘tacit knowledge’ used by lawyers. Second, it seeks to get to the heart of why frustration claims are so rarely successful by elucidating its doctrinal underpinnings