Learning that it's just as important to be authentic and have hard convos about what you want as it is to be accommodating. I used to say yes a lot, then harbour all this resentment. When people pissed me off, I didn't tell them and just vented to a friend thinking I would feel differently afterwards. What made me feel less anxious and more assertive was seeing the results of my work pay off. If someone took my alcohol at a party, instead of resenting/bitching about it until it happened again, I'd just say "hey when you took my alcohol on x occasion it made me feel resentful because I don't always like to share it. I'm not saying that this is the right way to think about it, but my preference would be that you ask first, and also plan to bring alcohol to parties if you plan on drinking." Basically, if someone pisses you off, invite them to take responsibility for what they did. How they react will tell you whether they value you. If someone says something I think is snarky, instead of ignoring it or responding with something snarky back, I ask them "hey when you said X, did you mean (insert what you think it meant)?" It taught me about the complexities of what angry people were thinking, whether they were directing their anger at me or nobody, and was in a sense reassuring. Now, when someone pisses me off, my conversations about it are more like "hey how should I bring this up with X?" Something very cool about being able to tell people what you want and them obeying, and not feeling guilty about it.