The plural of anecdote is not data and neither is the singular, but: I am ten years older than my partner, and this is my partner's first relationship. When we got together, we talked a lot about relationship failure modes and the hazards present in our situation (more than just the age difference), committed to voicing and understanding any concerns/fears/etc. that we experienced, and actually followed through on that commitment. We're only about a year and a half in, but so far this has been amazingly successful. It's hard to suss out how much is due to that commitment and how much is due to us apparently winning the compatibility lottery, but I do think there's a lot to be said for being realistic about failure modes and their likelihood. Long-term relationships, and especially cohabitation, require effort, and the sunk cost fallacy applies to them as much as anything else.
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.)