In order to satirize the die-hards, some people who accept the new calendar also send fake gifts to the die-hards on this day and invite them to participate in fake celebrations to make them fall for it. We will play tricks on each other on this day in the future, and it will become a custom after a long time. Then spread to Britain, the United States and other places, evolved into the present April Fool's Day.
Of course, in addition to this statement, countries also have their own versions of the theory of origin. For example, Christians say it is to commemorate Good Friday, while Greeks believe that April Fool's Day originated from the myth and legend of Demeter, the goddess of agriculture.