Assertiveness means standing up for yourself or others without diminishing someone else’s rights. It should be seen in contrast to passivity (which causes frustration, disappointment and diminishes your self-respect) and aggression (which causes anger, defensiveness and alienates the other party).
Being assertive will also help you stand out. Provided you don’t overdo it, people will appreciate the fact that you're a strong person. Assertiveness means self-confidence, and self-confidence radiates around you. Others trust you more, like you more and want to be around you.
Don’t complain, assert! Calmly express your feelings; say what you want to change and why, and how you would feel so much better if it did. Your goal is to explain how the other’s behavior is affecting you, not to act like a judge and jury. If you cause defensiveness, it’s likely you're not assertive (see verbal self-defense for how exactly to avoid causing defensiveness). This is why using ‘I’ language is a must. However, don’t overdo it! Too much ‘I’ language can make you seem egoistic. ‘I’ language can be replaced with ‘we’ language, but overdoing that will make you seem to be speaking for everybody (and again cause defensiveness).
