In his book “The Black Swan”, Nassim Nicholas Taleb states that this event can also be relative to knowledge.
As an example, a turkey gets fed for a thousand straight days, then on the day before Thanksgiving – boom, it is slaughtered. Here’s a diagram from the book that depicts before and after.
For the butcher, the event is expected, but for the turkey, the nonfeeding is a “Black Swan – an unforeseen event out of nowhere with no way to really predict its outcome (based on the previous behavior/data).
So let’s imagine the butcher being the ISP (such as Google or Yahoo) and the marketer or business as the turkey. Email deliverability and performance can be all good and smooth sailing, then out of nowhere – you’re in the tanker and messages are hitting the spam folder.
No more feeling of safety and what worked in the past no longer does… How could this be!?
Similarly, when it comes to email deliverability, the Black Swan event may be:
1) caused by a single event right before the dip in reputation (i.e. new low-quality subscribers added, a technical issue in the setup, emailing to a dormant segment, new email strategy, etc.)
2) your bad sending habits over time caught up with you and that was the day the algorithm decided to penalize you.
The hardest part for us email marketers is figuring out which of the two caused the “doom day”.
Was it a single event or was it something that was lingering for months?