I am new in statistical studies and on this site and I came across the "zero-sum property" in my book regarding the mean. It seems to be straight forward but I still can't understand the notion of it. The only information it gives with the formula is "the sum of the difference between each value of a variable Y, noted Yi, and the mean value of Y, noted as Y-bar, is equal to zero. Could someone explain the concept better? Thank you.