A "Black Swan" week...

During last week two particular events occurred that squarely belong to the "black swan" category.
Iceland's volcanic ashes spread across Europe, shutting down the airspace for most countries, leaving passengers stranded and further exacerbating the recovery of a weak and struggling airline industry. As no one was really prepared for this event and as no one really knows until when the European airspaces will remain closed (it will largely depend on the forces of nature), stocks of major airlines have taken a nose dive over the last couple of days. The repercussions could extend further into the European economy that is already struggling with a major debt crisis.
On a similar note, Friday's news that the U.S. Securities and Exchange Commission would be investigating the "venerable" Goldman Sachs for alleged fraudulent behavior led a major blow to a firm that, until then, had been boasting on its ability to boost the bottom line in any type of market condition. Again, no one was prepared, unless, of course, someone had access to insider information on the matter and decided to trade on it, which, in any case, would constitute fraud in most jurisdictions. The financial sector also took a nose dive with shares of Goldman losing close to 13% over a single day.
Although these two events are perfect examples of "black swans", I would like to emphasize that a "black swan" event can also very well be a positive one (these two examples just happen to be negative events) that would have the effect of lifting markets.
It should also be noted that positive and negative events don't carry the same weight in the human mind. According to studies on behavioral finance, a negative event can carry up to 2.5 times the impact on our psyche that a positive event would. Food for thought.