Building assertiveness skills is one of the most important things an individual can do. It affects everything. Unfortunately we aren't taught these skills growing up and assertiveness skills are often neglected in life. Usually passive aggression reins supreme.
Now I'm not saying that you need to go around picking fights 'being all assertive'. It is just in certain situations that you need to be assertive to maintain your sanity.
Two areas that I find that are particularly affected by assertiveness or lack there of is (1) Anger Management (2) Anxiety.
The ultimate irony with people who suffer from anger management is that they are horrified of confrontation. Just recently I had a professional fighter came in for anger management counseling. After speaking with him for a while, it emerged that he was horrified of confrontation, especially with his wife. So what happens is the he would avoid conflict and be a 'yes man' and it would build and build and then one day he would explode. Unfortunately his way of dealing with anger is to be physically aggressive. Which isn't on. This may also be one reason for domestic violence and abuse. Lack of assertiveness and inability to handle confrontation.
But people still get confused about when they need to be assertive. I say choose your battles and choose the big ticket items. Don't sweat the small stuff. For example, I had a client come in and was complaining about the state of the house and always having to 'nag' her husband and children to clean up. And she really focused on this. But the bigger ticket item for her was the lack of respect that other members of her family gave her and how they took her for granted. She never bother to talk to them about this bigger ticket item. Strange really.
I like to refer to them as defining moments. Defining moments when you need to be assertive and make an issue of something. Choose wisely because it takes effort to be assertive and make sure that it is related to you bigger ticket items. Other people like to refer to this as boundary setting as well. To know what your important boundaries are and be very clear when other people cross them.
Its hard because we don't like to say no and disappoint people. What will they do? They might not like us? They may never talk to us again. This is a fear of abandonment.
Building assertiveness skills is an important aspect of life and something that everyone should be mindful of.