A good, lightweight rule of thumb: before making a major life decision, spend at least an hour googling around for relevant information, especially from people who've done the thing you're contemplating. Chances are, your experiences will not be so different from theirs.
Then, seriously consider at least one alternative.
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.)