Assertiveness is the ability to stand up for your rights without being aggressive or passive. People who are not assertive usually let go of their rights and end up feeling bad.
Lack of assertiveness doesn't only result in accumulation of anger but it also degrades self confidence. There is a very strong connection between assertiveness and self confidence to the extent that a person could not become truly confident without being assertive.
Why assertiveness and self confidence are strongly connected I have mentioned before that self confidence is built when your subconscious mind observes your behavior and starts to trust you.
For example, if you managed to perform well in a certain sport several times your subconscious mind will start to believe that you are good at it and the next time you will play that sport you will feel confident.
But what does this has to do with assertiveness? If your subconscious mind kept finding that people are violating your rights and that you never stand up for them yourself confidence will degrade. On the other hand if you kept acting with assertiveness your subconscious mind will believe that you are worthy and you will become more confident.
How to have assertiveness and confidence:
In order to have assertiveness you need to:
Stand up for your rights whenever they are violated
Use confident body language (straight back, stretched shoulders and no arms crossed)
You must use "I" statement in order to appear confident for example "I can’t see because of your hat would you please take it off"
If you kept acting with assertiveness your subconscious mind will believe that you are worthy and you will become more confident.