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 had a related problem: performing a test without visualizing each of the potential outcomes.
I had been dating a guy long distance for about three months, and we were planning on moving in together. I had some reservations; my visits out there had been pleasant, but I wasn't sure that getting along for ~5 days at a time was that predictive of how well we would get along living together, and I had a bunch of specific doubts (such as his ability to have a difficult conversation in a way I felt comfortable with). I thought to myself "the way to deal with these worries is to give him a call." I did not think to myself "what would lead to me believing these worries, and calling off moving in together?" (Mistake 1.)
So, I call him, mention that I'm having some doubts and he explodes; everything's going terribly, and now also his boyfriend might be dumping him, and so I reassure him that I'm not dumping him and we're still moving in together, and that I had just been calling for reassurance. (This is why the mistake feels related: I made the decision during a high-pressure environment.) The call ends, and I realize "well, shit; that's basically confirmed my worries, and if I had planned ahead I would have known to call it off when he exploded." Then Mistake 2 happened: "I've already said we're going ahead with it, so I can't call him back and break up with him now."
(We broke up 3 months into a 12 month lease.)