Now am a witness of two Black Swan events since this blog started.... - 2008 Financial Crisis - 2010 Deepwater Horizon Oil spill What is a Black Swan Event ... " This was developed by Nassim Nicholas Taleb to explain 1) the disproportionate role of high-impact, hard-to-predict, and rare events that are beyond the realm of normal expectations in history, science, and technology, and 2) the psychological biases that make people individually and collectively blind to uncertainty and unaware of the role of the rare event." Or in more simpler terms an extreme outlier whose probability of happening is very very rare but when it does its impact is so huge that its pretty much shake's out the system and the assumptions. http://en.wikipedia.org/wiki/Black_swan_theory