If we do our standard deviations to the left, that's one standard deviation, two standard deviations. We know what this whole area is. The area, let me pick a different color. So we know what this area is. The area within two standard deviations. The empirical rule tells us, or even better, the 68, 95, 99.7 rule tells us that this area, because it's within two standard deviations, is 95% or 0.95, or it's 95% of the area under the normal distribution. Which tells us that what's left over, this tail that we care about, and this left tail right here has to make up the rest of it, or 5%.