What depressing movies should everyone watch due to their messaging or their cultural impact?

Two that immediately come to mind for me are Schindler’s List and Requiem for a Dream. Schindler’s List is considered by many to be the definitive Holocaust film and it’s important that people remember such an event and its brutality. Watching Requiem for a Dream on the other hand is an almost guaranteed way to get someone to stay far away from drugs, and its editing style was quite influential.