A single failure is a random failure plus its consequent effects which are assumed to occur during either a normal operational condition or in addition to an initiating event and its consequent effects.
天之道,损有余而补不足。是故虚胜实,不足胜有余。其意博,其理奥,其趣深,天地之象分,阴阳之候列,变化之由表,死生之兆彰,不谋而遗迹自同,勿约而幽明斯契,稽其言有微,验之事不忒,诚可谓至道之宗,奉生之始矣。-《九阴真经》