In the aviation world it is a pretty lame excuse to say "oh it dosen't happen that often so we can't be as prepared for it as we would like".
Better not practice those 4 engine failure drills in the sim then...or we better not have any of these terrorist attack contingency plans in place...don't really need to practice radar failure scenarios etc etc. It hardly ever happens. Jeez!
You can say those are extreme situations....but today a major international airport CLOSED because it wasn't ready to deal with an expected scenario...be it rare or not. If something is expected...it should be planned for! The plan was inadequate....and yet people are happy to find excuses for it.
To quote Rainboe
Better to take a couple of days of hell every so often.
Why?? Cos we can't come up with something better? We can't cope??
An airport dealing with 60 million passengers a year in a western country serving a MAJOR capital. A couple of days hell?? A couple of days embarrassment....again!