The gold standard is Six-Sigma - 99.99966% free of defects.
Indeed, but 6σ applies to the folk who step back a pace and contemplate the population.
For the individual on the day, the reality is more binary ... either you are in strife or not. From the perspective of standards, either the system accepts the population risk as acceptable (and the occasional mishap as inevitable) or provides some semblance of training (admittedly at a cost) to give the individual some reasonable hope of employing the cognitive things which humans are good at.
Like PJ2, I hold the view that a bit of sim time for crew exposure to the improbable may (not necessarily will) provide some benefits.