Great new installment of the 1-minute MBA from D^2.

Another universal rule I'd like to add, although not applicable to the shooting incident:
we are only ever prepared for the catastrophes that have already happened.
This isn't of course a criticism but a basic constraint.

For example: you could see policemen patrolling the tube yesterday in case they blew it up on a Thursday again. And security is pretty tight for airport bagages! The 9/11 attacks managed to hit the Pentagon, which many would consider to be one of the most protected buildings on the planet.
Of course a repeated terror attack has a very powerful effectand that's what they did in London, but in general surprise is their greatest asset. And in general, catastrophies must be considered as random events, essentially unpredictable.

But to tie in with what d2 says, it's even more idiotic to push for zero risk in an area where heuristics will tend to be wrong, because biased towards past occurrences. The risk assessement must consider the diffuse and subjectively random nature of these disasters: hence the importance of soft, low-level approaches... and the ridiculous nature of the strident, panicked calls for "strong measures!!" to be taken.

Relatedly, what will happen when Al-Qaeda (or an offshoot) recruits an angry black- or white-skinned Muslim? If he doesn't look Arabic, he will not likely be stopped... It's quite likely, actually surprising it's never happened before. Just imagine a slightly insane follower of Malcom X (I've met one once).