各位大佬，请问一道有关OLS斜率系数的判断题：
For an OLS regression of y on x, observations for wich x is far from its mean will have more effect on the slope estimates than observations for wich x is close to its mean value.（这是北大计量经济学期中的一道原题）
如果大家能够给出简单的证明或者反例就更好了，谢谢