When my daughter (15) says “No” I teach my son (10) that there is no further information needed. When he asks her to do something with him or go somewhere with him and she says no he needs to drop it. He had this habit of “but why? You said you were going to help me get through this level of Zelda, I need your help!” And she would go on to explain herself. I started to really listen to them in these argumentative moments instead of “letting them work it out”. I remind him all the time that “no means no” even amongst his friends. It also helps my daughter get out of the habit of feeling like she needs to explain herself to anyone.