This is a repository for major, life-altering mistakes that you or others have made. Detailed accounts of specific mistakes are welcome, and so are mentions of general classes of mistakes that people often make. If similar repositories already exist (inside or outside of LW), links are greatly appreciated.
The purpose of this repository is to collect information about serious misjudgements and mistakes in order to help people avoid similar mistakes. (I am posting this repository because I'm trying to conduct a premortem on my life and figure out what catastrophic risks may screw me over in the near or far future.)
That would also apply to not having any friends outside of your country, or outside of your generational group, or outside of your socio-economic class, or ...
Also, “all kinds of interesting things” have opportunity costs.
I do have friends in all those groups, and consider them valuable as learning experiences in addition to the friendship. If you want to know people, cast a wide net. And knowing people has more value than you might think - politics, sales, even picking a neighbourhood to live in are all fields where a better understanding of human nature can be very valuable.