" The beauty of the normal distribution - its Michael Jordan power, finesse, and elegance - comes from the fact that we know by definition exactly what proportion of the observations in a normal distribution lie within one standard deviation of the mean (68.2 percent), within two standard deviations of the mean (95.4 percent), within three standard deviations of the mean (99.7 percent), and so on. "

― Charles Wheelan , Naked Statistics: Stripping the Dread from the Data