Being nice to everyone makes you happy for life, even if 20% of them ended up not nice to you, which you can consider your cost. The deviation of such a cost depends on your social networks.

与人为善是快乐人生的秘诀,哪怕他们当中有20%对你不好,你就当这是你的成本。这项成本大小取决于你所在的社交网络。