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.)
I will second this but with a twist: I tend to look really weird. But looking really weird and FANCY makes for a lot better and fun random social interactions. Put effort into your appearance, decide what you want to look like and what image you like to project, but that image doesn't have to be optimized for muggles unless you want it to be.
Wizards who don't learn to interact profitably with muggles cut themselves off from most people in the world. Cutting yourself off from most people in the world is a life-altering mistake.