It seems to me that 'multiple failure' is a basic problem in all walks of life, not just database issues.

I missed the meeting because (perm any three)

I got up late

Lost the car keys

Car wouldn't start

Accident on the motorway

Went to the wrong office

Had the wrong time for the meeting

Child was ill and had to be taken to doctor

etc etc.

So, in real life, and in the database world, there are many scenarios that we can plan for, and some combinations. Often we'll do this 'seat of the pants', but depending on the price of failure, will enumerate the possibilities and mitigations more carefully. But there could always be some set of circumstances we haven't thought of or which are just to expensive to mitigate for the price / probability which will lead to failure.

As database professionals we need to have enumerated the likely failures, mitigations and costs (of mitigation and failure) and put appropriate things in place (and tested at least some of them) and have a coherent plan that looks reasonable and defensible before, and hopefully after, a disaster.