I agree that other than a seat-of-the-pants feel that my subsystem's are robust (in the sense of avoiding failure), I have no quantitative measure of my system's "safety Margin". 

 Would certainly be interesting for everyone to take the 0-10 exam on their system and report the results of the assessment.  Perhaps we might find those above a 5 and give them some careful study.

The problem, of course, is that with a one-of-a-kind system ‘guessing’ at a number from 1 – 10 is not much  different than ‘guessing’ that your system is OK in regard to a given condition.  The only way to get a numerical rating is to have a large number of systems tested to failure for a number of different variables.

Al G