Reading the article about Japan’s Nuclear reactors and the issues the country is now facing because of a number of critical failures that occurred; with this post I would just like to point out how this, in a similar fashion, applies to computer security.
Bill says “As we learned in the global financial crisis as well, instruments and devices thought of as separate entities can all “go south” as the result of a single underlying cause, upending estimates of how serious and consequential any one failure would be.” 
Focusing on the all it takes is one failure, which in turn will kick things off, will or can lead you to a chain reaction of undesirable events occurring after that. Be that a specific vulnerability, a weak password etc being the failure point, if all possible matters are not looked at in depth, reviewed and addressed (e.g., penetration test) appropriately then information can go missing and systems will get compromised.
Many a times it is hard to explain to people what the consequences are when the failure does occur and how it will affect them in the long run. In this case with the nuclear power plants the consequences are quite dire for the population (short and long term). Whereas in the computing realm only unless the issues cross into the physical realm (e.g., lost work hours leading to lost revenue, products can not be delivered etc.) do people start to pay notice. Demonstrating the short sighted on look onto long term effects of possible consequences.
 – Japan Nuclear Accident: Worse than Worst, Again by BILL SWEET – http://spectrum.ieee.org/energywise/energy/nuclear/japan-nuclear-accident-worse-than-worst-again