The Law of Diminishing Returns, true in life as well as in story, is this: The more often we experience something, the less effect it has. Emotional experience, in other words, cannot be repeated back-to-back with effect. The first ice cream cone tastes great; the second isn’t bad; the third makes you sick. The first time we experience an emotion or sensation it has its full effect. If we try to repeat this experience immediately, it has half or less than half of its full effect. If we go straight to the same emotion for the third time, it not only doesn’t have the original effect, it delivers the opposite effect.
Suppose a story contains three tragic scenes contiguously. What would be the effect? In the first, we shed tears; in the second, we sniffle; in the third, we laugh… loudly. Not because the third scene isn’t sad – it may be the saddest of the three – but because the previous two have drained us of grief and we find it insensitive, if not ludicrous, of the storyteller to expect us to cry yet again. The repetition of “serious” emotion is, in fact, a favorite comic device.
McKee, Robert. Story: Substance, Structure, Style, and the Principles of Screenwriting. HarperCollins e-books, 2010: 243. (via justanotheridijiton)