The mean and median are both measured of central
tendency.
The mean and the median are the same for symmetric distributions. In general,
the mean will be higher than the median for positively skewed
distributions and less than the median for negatively skewed distributions.
Change the above distribution's skew and see the effect on the relative size
of the mean and median.
The mean is more affected by extreme scores than the median and is therefore not
a good measure of central tendency for extremely skewed distributons.