Some people didn't want the date to changed or they had trouble remembering the new date. Those who were caught celebrating on April 1 were then called "fools", thus the birth of April Fools Day.

The day has changed through the centuries and now we play jokes on each other, making FOOLS of others. April Fool pranks, should always be in fun and not to harm anyone. The best jokes are ones that make people laugh, not cry.