A is for aphorism - is it true that 'a careful history will lead to the diagnosis 80% of the time'?

Medicine is an uncertain pursuit. As medical students and junior doctors, we often try to manage this by collecting golden rules as we progress through our education. And there are many occasions when a 'third voice' joins us during a consultation - the voice of a professor, clinical tutor or colleague, that enters our head spouting a pearl of wisdom, such as, 'a woman of childbearing age is pregnant until proven otherwise' or 'when you hear hoof beats, think horses not zebras'.