We can never know if there are additional hidden deficiencies in our systems due to unknown or unexpected interactions between parts in the system. We cannot know if your postulated initiating events give a sufficient coverage of the space of possible events that may occur. We may however argue that many of the unknowns we know about, often are less serious than the challenges that have been considered in the design basis accident or design basis threat (DBA/DBT) scenarios. That will leave us with the unknowns we do not know about. To some extent even scenarios we do not know about may, according to the thinking of resilience engineering (Hollnagel et al., 2006), be acted upon by general measures installed in the control loops.