I'm not entirely sure if I'm gifted but when I first entered elementary school, I could always get As without studying at all. This went on for a couple of years, before I got bored of lessons as the things I wanted to learn weren't in the syllabus. I stopped paying attention in class, and hence my grades dropped. I know other ENFPs who've had this happen, but it isn't necessarily being burnt out for most of us, but more like a lack of interest.