I'm confused. I got that what I was relating behaviorally to Ni, isn't Ni. So I don't get the further analysis on how my Fi affects my Ni...because isn't what I said, invalid now?The reason why Ni stresses you out is because of your introverted feelings function is a subject that is subjectively influenced by the events that you imagine from within and from external events. If is a feeling subject that truly experiences feelings deeply so that experience stresses you out. I don’t know if your sister too gets stressed out as you and I would since we have Fi unless you ask her. Maybe their let live attitude and you can’t influence what happens let’s them not personally feel or associate feelings to the stressful events.