"No matter what actually happened, you should've been prepared."

This is just plain false. Being prepared comes at a cost. If you over-prepare, then your customers have to pay more for no good reason, and they don't necessarily want to. You have to draw a line and make a judgement call.

There are such things as natural (or political) disasters so serious that it would be extremely stupid to plan for them. And there are other disasters in between this and run of the mill. Again, it's a judgement call. And it's not your "fault" if the customer wants a combination of low price and reliability, and you made a reasonable tradeoff in order to achieve it.