The principle of parsimony, known to many as Occam’s razor, states that simple explanations are preferred over more complex ones where explanatory power is equivalent. An enduring maxim in science and philosophy, it is also commonly used implicitly when non-scientists reason about everyday problems. In medicine, the principle of diagnostic parsimony favours a unifying diagnosis over multiple ones where both explain the clinical data equally well and is arguably the most widely employed heuristic in medical practice.