There was a rabbi named Gedalia Something [his last name is debated by scholars] who decided that Jews ate too much on Rosh Hashana. So in order to give our digestive tract a WELL NEEDED break, he decreed a fast.
Thank G-d!!!
He tried to decree another after Sukkos [when we REALLY need it] but it wasn't accepted b/c two fasts in Tishrei are enough.
Mussar Haskel: Go easy on the food. Being overweight kills more people than Corona killed [in the long run] and causes a HOST of health problems on the way.