Black swan events: unforeseen, unanticipated, and catastrophic issues. These are the incidents that take our systems down, hard, and keep them down for a long time.By definition, you cannot predict true black swans. But black swans often fall into certain categories that we've seen before. This talk examines those categories and how we can harden our systems against these categories of events, which include unforeseen hard capacity limits, cascading failures, hidden system dependencies, and more.