Assertion is not a trait that people are born with. It is something that is learned and developed over time. It is also dependent upon the individual and situation - people react differently to different situations. The same incident may cause one person to respond in an aggressive manner, while someone else may be passive, while yet another person may be assertive.
Even if you think that you are 'too passive' or 'too aggressive' and don't know how to be assertive, chances are, you do respond assertively to at least some things in your life. For example, you may feel comfortable speaking up when a cashier in a store gives you the wrong change, but you may not say anything if a waiter in a restaurant brings your food late or cold. The trick is to recognize those areas where you are assertive, identify your skills, and apply them to other areas of your life.
Everyone can expand upon their assertiveness skills, no matter how limited they think they are. You just need the desire to change your behavior and value yourself more. Ask yourself these questions:
If your answers to the questions above are "Yes", then you are already on your way to being a more assertive person!