Relief

We experience many real-life situations that are so ironic or tragic, that they become almost unbelievable. During these times, we can either totally stress out or laugh. Stressing out would bring us closer in to the situation, zooming in on the problem. Seeing the humorous side provides us with a detached perspective, and thus helps us to cope.

The actual story/situation creates tension, and tension also results as we try to cope with two sets of emotions and thoughts. We need a release and laughter is the way of cleansing our system of the built-up tension and incongruity.

This makes perfect sense when we apply it to movies. Sometimes, in highly tense movies (e.g. action/thriller types), the director uses comic relief at just the right times. This is carefully calculated: he builds up the tension/suspense as much as it can be, and then breaks it down slightly with a side comment, allowing the viewer to relieve himself of pent-up emotion, just so that the movie can build it up again. Quite a crafty business!