Having worked with hundreds of women to find peace and rediscover their authenticity, I can say that this is one of the absolute toughest and most important lessons to learn. And this goes for any kind of relationship -- partner, friend, co-worker, family member, you name it.
In relationships, freedom comes from two things:
1) Learning to use your voice and assert how you feel and what you need, and then...
2) Letting go of the outcome.
Many people grow up in families where this process is stunted, because doing#1 is not okay. This is tough, because parents DO set the rules and boundaries, so naturally, kids feel like they don't always have a voice or have choices. That's part of growing up. But as a child matures, if their opinion is not given value, if they do not feel safe or encouraged to express how they feel and what they need, they learn to keep that in. While this most commonly happens in the family of origin, that's not always the case. It could be learned in an abusive relationship or in a bullying situation, too.
So, if you've learned to not talk about what's really going on with you, you'll find other ways to passive aggressively communicate that very often end up hurting you in the long run. Many of my clients communicate via their eating disorders or addictions. We practice assertive communication all the time-- and usually they hate it. Not only does it go against family messages in many cases ("sweep it under the rug," "don't ruffle any feathers"), but there's also the cultural message that "emotions are a sign a weakness, and weakness will get you hurt."
First, you have to determine what your own beliefs are around expressing what you really need + feel, where they came from, and how they're working for you. Next comes the hard part of practicing confrontation and assertiveness, even when it feels totally foreign and uncomfortable at first. I've seen women make amazing progress with this even just in the one, two or three months they're with us. It can be difficult at first, which is why it really helps to have a therapist or coach walking through it with you. Sometimes if you've been suppressing your voice all your life and you suddenly start using it, it may be difficult to find that line of "assertive" versus "aggressive."
Let Go of the Outcome
And then, of course, comes the difficulty of #2 -- "Okay, you're telling me to use my voice, and I am, but it's not WORKING! Nothing is changing!"
The power does not come in someone else changing their behavior. It comes from speaking your truth, AND being able to let go of the outcome. Now, of course there are going to be situations where if you speak your truth and nothing changes, then you may have some hard choices to make about what you need to do. (You told your friend you're frustrated with being flaked on after the 5th time, and she's still doing it? Maybe it's time to move on from the friendship.) So, if you learn to do #1 but aren't doing #2, you'll continue to feel trapped and frustrated.
Finally, a disclaimer on this one: I'm really talking about letting go of the outcome in our one-on-one relationships, not at a cultural level. I think we have to use our voices until the cows come home in order to create real change in the world on a broader scale.