It is true that the complement will be an unusual event
when an event is almost certain to happen. The complement of any event A is the event [not A] in probability theory, i.e. the event that A does not occur.
An event whose probability is small is
called an unusual event. The most commonly used value is 0.05, in other words,
an unusual event is a probability less that is than this value, and the cutoff
value can be any small value that seems
suitable.
Let’s take this for example:
It can either land showing “heads”
or “tails” if a typical coin is tossed and one assumes that it cannot land on
its edge.
