What is a fool? I think of a clown or silly person, someone not so smart or a joker. So why do we have a holiday celebrating this kind of person? Maybe just an excuse for playing tricks on others, etc.? I found this online:
Unlike most of the other nonfoolish holidays, the history of April Fool's Day, sometimes called All Fool's Day, is not totally clear. There really wasn't a "first April Fool's Day" that can be pinpointed on the calendar. Some believe it sort of evolved simultaneously in several cultures at the same time, from celebrations involving the first day of spring.
The closest point in time that can be identified as the beginning of this tradition was in 1582, in France. Prior to that year, the new year was celebrated for eight days, beginning on March 25. The celebration culminated on April 1. With the reform of the calendar under Charles IX, the Gregorian Calendar was introduced, and New Year's Day was moved to January 1. Source
I don't like the idea of practical jokes like replacing the sugar with salt-I did that once as a young girl to my family, but perhaps having a better sense of humor would be helpful to all of us on this special strange day.