What does it mean to be planning for the unexpected? Something out of the blue which we failed to foresee, how could we be planning around this?
Firstly, the unexpected might not be unheard of. We don't expect all engines of a jet plane to fail at the same time, but we know this has happened.
Secondly, let's differentiate between cause and effect. Our office might suffer a power outage. We can think of possible causes for this effect, but we won't know them all. Still, if we can imagine the effect we can plan around it.