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Butterfly Effect
This is really more of a physics/chaos theory, but it does relate to psychological as well, so here goes. The butterfly effect serves as a metaphor for life in a chaotic world. Specifically, it suggests that small events can have very large effects. This is a relatively new approach as it was once believed that small events produced small effects and large events produced large effects. Chaos theory, however, changed this view and now the butterfly effect suggests that little things, like a bird flapping its wings over China today, can have big effects, like causing a hurricane in America next week.
