In this video I answer the common question of why we divide by n-1 when calculating variance from a sample, known as Bessel's Correction. I focus on conceptual understanding of why this adjustment is needed and why n-1 is the appropriate adjustment on average, rather than making up a population and possible samples to illustrate this. I show why x-bar (the mean of the sample) tends to underestimate the squared deviations, then provide 2 arguments for why n-1 adjusts for this; one based on degrees of freedom, and the other based on trying to estimate the average amount of bias of the sample variance.