I've known so many people who "have it all" by society's standards but who are miserable because no matter how much they achieve, they never feel like they're successful enough. I don't want to live like that.

Sorry I don’t agree with this at all, not everybody feels like their life needs to be a constant struggle to find it interesting and meaningful.

I think it depends on the person and the culture in your workplace. In my workplace I think you get rewarded more for advocating for yourself and making yourself seem more powerful and respected, than by letting people underestimate you.

Talk to them tomorrow and say “In the meeting yesterday, I felt surprised when you brought up idea X as your idea because I recall coming up with it myself. I was disappointed because I felt like you should have acknowledged my role in coming up with this. What are your thoughts?”

Their response to this should tell you whether it was an innocent mistake or them actually trying to take credit for your idea. If the former, then you’re all good - use this as an opportunity to build more relationship with them. If the latter, make it clear that you don’t want it to happen again, and know to watch out for them in the future.

Absolutely, but it goes both ways. Sometimes you try to tell people you’re not interested and they don’t want to accept it.