The art in assertiveness is to ask strongly for what you want then to let go of it if the answer is No. You tread the fine line between consistent perseverance and the stubborn persistence that can feel to others like abuse. Passive people do not ask for what they want. Aggressive people demand (openly) or manipulate (secretly) to get what they want. Assertive people simply ask, without inhibition of themselves or pressure on others.
— "How To Be An Adult" by David Richo