2014 CFAI L1 text Vol 4 P.296~297 and the concept of skewness introduced in QM
It is stated in the last paragraph :
… whereas Exhibit 9 demonstrate the negative skewness of stock returns by ploting a histogram of U.S. large company stock returns for 1926~2008, Stock returns are usually negatively skewed because there is a higher frequency of negative deviations from the mean, which also has the effect of overestimating standard deviation.
My questions :

Is it that the mean in Exhibit 9 is zero ?

Why there is a higher frequency of negative deviations from the mean (in Exhibit 9) ?

Why it has the effect of overestimating standard deviation ?