Re A (conjoined twins) indicated that Gracie was the stronger sibling who was sustaining the life of Rosie. Rosie had only survived birth due to a shared common artery that enabled her sister Gracie to oxygenate blood for both twins. If surgically separated, Gracie had a 94% survival rate, but Rosie was guaranteed to die. However, if they were left conjoined, then Gracie's health—which was already rapidly deteriorating—was predicted to fail before they were six months old. Gracie's death would inevitably result in Rosie's. At first instance, Mr Justice Johnson was left to decide the case without any direct precedents to guide him but
There are known knowns management and strategic planning circles. Known unknowns refers to "risks you are aware of, such as cancelled flights..." Unknown unknowns are risks that come from situations that are so unexpected that they would not be considered. "For example, prior to the invention of the personal computer, manufacturers of typewriters probably didn't foresee the risks to their business". Contemporary usage is largely consistent with the earliest known usages. For example, the term was used in evidence given to the British Columbia Royal Commission of Inquiry into Uranium Mining in 1979: The term also appeared in a 1982 "New Yorker" article on