This. I see that if you have one and only one chance to push the Big Red Button and you're not allowed to use any preliminary testing of components or boxing strategies (or you're confident that those will never work) and you don't get most of the experts to agree that it is safe, then 90% is more plausible. If you envision more of these extras to make it safer--which seems like the relevant thing to envision--90% seems too high to me.