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
> $Y_i$, and the mean value of $Y$, noted as $\bar Y$, is equal to zero.

Could someone explain the concept better?