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.)
First, excellent idea!
Second, where do I start... Am I the only one who can list at least half a dozen life-altering sub-optimal decisions without pausing to think? Nothing catastrophic, though. I'll only mention a few school-related ones.
Undergrad: yielding to pressure to go for a comp. eng. degree instead of physics and not talking a chance to switch when one was available. Sure, employment options and salary are way better in comp. eng., and I never hated the work. But I will never find out whether I could have been a top x% scientist, rather than a somewhat-better-than-average programmer.
Grad school:
Waiting too long before going back to school. Could and should have done it 8-10 years earlier. Bad for several reasons: older means harder to learn and less competitive for postdoc positions, less mobile means fewer school choices, used to higher income means harder to downgrade. "A luxury, once sampled, becomes a necessity".
Overestimating my mathematical abilities when picking a PhD research topic (and a supervisor) after a successful and enjoyable Masters. As a result, I ended up with a mediocre thesis and no easy career path in academia. Aggravated by occasional professional and personal conflicts with the supervisor, who was not known for promoting their grad students to begin with. Watching someone with a very similar skill set do extremely well after picking a less risky path shows what could have been.