Authors:

Let others know when they have hurt or angered you. By not speaking up when someone insults or mistreats you, you are inadvertently giving permission for him or her to continue to treat you in the same way in the future.

Beverly Engel (2011). “AARP The Nice Girl Syndrome: Stop Being Manipulated and Abused--and Start Standing Up for Yourself”, p.4, John Wiley & Sons
Let others know when they have hurt or angered you. By not speaking up when someone insults or mistreats you, you are inadvertently giving permission for him or her to continue to treat you in the same way in the future.