As a rule, I don't make "close" friends with people I work with. Falling out with people is a real thing, and getting judged for things that are in my private life (whatever they may be) is not something I want to deal with 40+ hours a week.

With normal friends, I can at least avoid them. Co-workers? Not so much.

I'm nice, I'll socialize, but I won't share or divulge any detail of my private life.