On most days, pulling a harmless prank, or two, on family members would result in a time-out. However, on April 1st, aka April Fools' Day, lighthearted tricks are both expected and welcomed. The origins of the tradition are hazy. Some believe the fun began in 1582 when the world transitioned from the Julian calendar — which ushered in the New Year on the last week of March — to the current Gregorian calendar. Those unaware of the change, or refusing to accept the January 1st start date, were often pranked on December 31st. Others maintain the ritual began as a joyful way to welcome spring.