A manager of a day$-$care center in Haifa, Israel has a clearly stated policy that parents are supposed to pick up their children by $4$pm $(16$:$00).$ But often parents are late. Each week, there is an average of eight late pickups. To combat tardiness, the manager of the center instituted a fine of $$3$ per child per incident. Surprisingly, the number of late pickups more than doubled, to twenty per week. Why?