The principle of safe fail in all its different applications (far from all of which have been mentioned here) is yet another example of how the uncertainty aspect is inherent in the concept of safety.
Admittedly, meaningful probability estimates may be possible for some, perhaps most application of the sub-principles mentioned here.
Yet, as should now be clear, even so, the purpose of these methods is not only to reduce probabilities of possible negative events that have been foreseen and for which probability estimates have been provided.
In addition, uncertainty reduction is an important objective.
We can call this the Titanic lesson. We now know that the Titanic was far from unsinkable.
But let us consider a hypothetical scenario.
Suppose that tomorrow a ship-builder comes up with a convincing plan for an unsinkable boat.
A probabilistic risk analysis has been performed, showing that the probability of the ship sinking is incredibly low.