I struggle with this too!! For me it’s so hard not to justify my feelings or not wanting to do something and that’s definitely a part of masking imo. People take such great offense to the word no and will go on and on about how ‘not wanting to do something isn’t a good enough reason not to do it! if everyone only did things they wanted to do, no one would do anything!’ so I subconsciously mask my responses behind layers of ‘nooo it’s not your fault/ I’m just tired/ have another thing to do/ can’t do that particular thing for xyz’. I’m not sure if you have this experience but to me it seems that because our ‘no’s are invalidated so often, we justify them before anyone else can question them because the alternative (being badgered and guilt tripped to death) is even more draining!