It doesn ' t have to but it helps if the ambiguous ending leads to to form ideas in your mind about what will or did happen . It ' s hard to explain but basically be openended and give you some direction in terms of what could happen , not be completely openended where you have no idea exactly what to imagine . You should not be thinking That ' s it ? It ' s over just like that ? Now what ? It should cause you to think That ' s it ? I wonder what happened in terms of . or how . played out . Be a good ride up to that ambiguous ending . You aren ' t gonna judge the film ' s storytelling simply based on its ending . Yes Incoherent Vice had a messy and poor ending as another person pointed out but what about everything which led up to it , that wasn ' t as bad was it ? I ' m not saying don ' t criticize the ending but I ' m not gonna criticize a film just because its ending ' didn ' t work for me ', I have to look at the whole body of work . It helps if it conveys some sort of meaning or significance by being openended and not just doing it for the sake of it because it ' s the lazy thing to do . You often feel the film giving power and being in control with a good openish ending .