Assertiveness is a valuable character trait that empowers us to express our thoughts and feelings confidently without being aggressive. In contrast, an un-assertive person can be timid, indecisive, and prone to being taken advantage of. The opposite of un-assertive is assertive, which means being authoritative, bold, or confident. Other antonyms for un-assertive are determined, powerful, self-assured, self-confident, and strong-willed. While being un-assertive can sometimes lead to negative consequences, being assertive can be advantageous in communication, relationships, and personal growth. It is always a good idea to seek a balanced approach, where one can be assertive while also respecting the needs and opinions of others.