It does not infringe on the rights of others or rely on guilt for results. Assertiveness starts with the premise that each human being is given rights that do not depend on status or performance. You have the right to express your perspective. You have the right to assume personal responsibility and to decline responsibility for others. How you govern yourself in relation to these rights is important for valued communication.
Communication is valued when both parties, the sender and the receiver, are respected.
The difference between passive, assertive, and aggressive communication rests with the exchange between parties and quality of the message. Passiveness diminishes your capacity to be heard and validated. Aggressiveness exerts differential power to promote a certain end result that is not based on mutual respect. Only assertiveness respectfully engages both parties for valued communication. Self-confidence is projected, not performed.