  Black swan events are statistically rare occurrences that carry extremely
high risks. A typical view of defining black swan events is heavily assumed to
originate from an unpredictable time-varying environments; however, the
community lacks a comprehensive definition of black swan events. To this end,
this paper challenges that the standard view is incomplete and claims that
high-risk, statistically rare events can also occur in unchanging environments
due to human misperception of their value and likelihood, which we call as
spatial black swan event. We first carefully categorize black swan events,
focusing on spatial black swan events, and mathematically formalize the
definition of black swan events. We hope these definitions can pave the way for
the development of algorithms to prevent such events by rationally correcting
human perception
