Linear art forms such as music, film, and fiction present pictures of change. We start at point A and end at point Z. One interesting twist on this is to end early, at point S, where we are pointed at Z and yet have a ways to go.
This approach trades away satiation of the audience's expectations and leaves them with an anticipation of those expectations being fulfilled.
At the end of Mike Nichols’s film The Graduate, Benjamin comes to rescue Elaine from the world of their parents and their twisted mores. Consider that the film could have ended a little later, as they arrive at some destination and perhaps try to have a life together. Ending in motion by way of the bus ride emphasizes the film’s true theme: liberation.
The end of Good Will Hunting also dwells on escape. Viewers know Will has decided to go find his former girlfriend Skylar, who lives on the other side of the country. The film could have ended with Skylar answering her doorbell, finding Will on her front step, and their final kiss. But the film's actual ending leaves viewers with anticipation of that moment, and this is important because more than he needs Skylar, Will needs to open himself to new possibilities. This final wide shot of Will’s car disappearing down the highway emphasizes precisely that. He is in motion as the whole world stretches out in front of him.
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