I'm pretty sure a significant part of altruism is signalling that you'd be a good parent and make it so you can get in a relationship and have kids
8-0 That, um, doesn't look like the empirical reality I'm familiar with. Sure, no one likes me-me-me assholes, but you certainly don't need to be altruistic to get someone to marry you.
What is something you used to believe, preferably something concrete with direct or implied predictions, that you now know was dead wrong. Was your belief rational given what you knew and could know back then, or was it irrational, and why?
Edit: I feel like some of these are getting a bit glib and political. Please try to explain what false assumptions or biases were underlying your beliefs - be introspective - this is LW after all.