I understand that "I" am not helped by altruism, but that my replicating genes are. In most cases, I and the replicating genes are helped by the same actions, thus self-interested actions generally "work".
Altruism happens when the replicating genes' benefit outweighs my own.
Unless you're talking about cases where you're being altruistic to your family, I'm pretty sure the main reason being altruistic is good for your replicating genes is that it's good for you. 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, but if you want a relationship, it's good for you.
In any case where you know you're not helped by altruism, doing it shows that you're not just acting in conscious self-interest.
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.