Nassim Taleb, author of The Black Swan, defines this metaphor as a highly improbable event that has 3 characteristics: It is 1) unpredictable 2) it carries a huge impact; and 3) after the fact, humans want to concoct an explanation that makes it appear less random. For example, Google is a Black Swan. They just celebrated their five year anniversary, and their stock continues to trade above $575/share. You could say that Barack Obama's highly effective, viral online presidential campaign was a positive black swan. The September 11, 2001 events exemplified a negative black swan.
Sometimes, you just have to let the positive black swans (serendipitous events) unfold, sit back, and enjoy the ride.
Last Wednesday, mother nature presented me with a black swan. As I was preparing for a very busy day in the office, 42 elk interrupted my schedule.