This is a great article from A Life of Productivity about the rules of 3. Below is the excerpt… you can read the full article here:

For some strange reason, our brain is wired to think in threes. As kids, we grow up immersed in stories that involve threes: Goldilocks and the Three Bears, the Three Blind Mice, and the Three Little Pigs. In high school, when we’re forced to dissect books like The Three Musketeers for English class, we break down the plot into three parts—the beginning, middle, and end. When we become adults, we observe that good things happen in threes, and that the “third time’s the charm.” The Olympics awards three medals for each event—gold, silver and bronze… READ MORE >