No one is ever cheerful the day of The Lottery, however very few truly know the reasoning behind the day.
Once a year, the man of each household must draw from the black box. On one of the papers inside the box, there is a black dot. He who draws this paper must have their entire family/household draw.
This year, Mr.Hutchison had drew the black dot. Everyone in their family had to draw from the box, even little Davey. Out of the family, Mrs.Hutchison drew the black dot... meaning she must be stoned to death.
The people in the village stoned Mrs.Hutchison to death.