"April Fool's Day" is a lying festival that appeared after the religious revolution in the 15th century AD. At that time, Philip II, the king of Spain, established a "heretic Inquisition".
As long as he was not a Catholic, he was regarded as heretic and was sentenced to death on April 1 every year. The subjects feel very terrible, so they take lying and joking as their pleasure every day to dilute their fear and hatred of the rulers. Since then, it has been used for a long time and evolved into today's "April Fool's Day".