The purpose of assertiveness is social cohesion, basically it allows us to be together in close proximity even if we are disagreeing on certain things without wanting to strangle each other.
You don't necessarily have intimacy in this scenarios, where there is a lot of disagreements between two or more people it is hard to be yourself uncensored in their presence, you have to self censor yourself for the sake of the group.
Assertiveness, it is part of your self preservation instincts, if you need to assert your needs it means that they are under a certain degree of attack from the outside. So generally speaking behind assertiveness there is anger, if the individual that is being under attack considers the group to be of any benefit to himself, he is going to suppress his anger and tolerate the inconvenient.
However sometimes we are confused of the benefits that we receive from others, so we censure our anger and tolerate the inconvenient for absolutely no gain. Then this is an unfair exchange, and it becomes abuse.
To restore your ability to be assertive and express your anger, you almost have to see the world in black and white. Things either help you or not.
Passive people will dig themselves in a corner by confusing themselves, generally speaking the inner dialogue goes something like this: "this is good because x reason, but on the other hand it is also bad because the y reason". The conclusion being that the situation is so bad that is good.
So then off course that when the logistics look like that the best course of action is inaction. In order to act you need clarity, the conclusion needs to be very clear this is good, I should continue it or this is bad, I should stop.
As always the explanation to all irrational behavior is anxiety, the reason why people do this is to control their anxiety of making a bad decision to stop themselves from taking any decision at all.
Taking decision unfortunately is inherently painful, all decision that you will ever take will lead to regret. This is why it is impossible to avoid the pain, if you don't act you will regret that you didn't and if you do regardless how it goes, you will regret that you did or that you didn't do it differently.
It is only when you accept the pain of making a decision that it will stop paralyzing you, in realizing that you can't avoid regret you set yourself free. Not from regret itself but from your inability to decide.
