If you don't stand up and say something, you can't rely on someone else too. Being your own advocate is important every day. Whether its in regards to your feelings towards another person, your own personal values, or just to get your wants and needs met, you have to say something yourself. I have talked to people that think others can read their minds and know what they want, or expect people to anticipate their needs. First off, thats not fair to the other person, and secondly you'll spend a lot of time being upset.
You want to value your opinion by sharing it, by honoring yourself and to not stay quiet when something you're passionate about is brought up. There is a DBT skill called FAST that stands for be Fair, no Apologies, Stick to your values and say your Truth. In other words, be respectful to others and yourself when sharing your opinion by not bashing others and honoring your own. Don't apologize for having an opinion or for your existence, its valid and important and so are you. Act in a way that respects your boundaries and your values by not compromising them or allowing others to disrespect them. Finally, always be truth in what you say, especially if you want to be heard by others and feel aligned with yourself.
If you can practice these techniques when in conflict, conversation, or in your own mind you'll most likely feel more proud and accomplished because you were able to honor others while honoring yourself.
Look at what these teens from Parkland High are saying and doing with there platform. https://www.nbcnews.com/news/us-news/parkland-shooting-victim-maddy-wilford-speaks-out-following-hospital-release-n851286