I experience my fear rarely, it only comes up after my mood turns horrid and my defense mechanisms sort of fail, because there's this sort of protective film that reminds me of my achievements and potential to counteract the fear. However, when I experience it, it's in a similar way to what you described. I'm of the heart-triad mindset that you need to prove yourself and distinguish yourself in some way so people don't replace or forget you. I feel like I can't reach my idealised self, that nothing I do will be enough, and thus I'll never be enough.

It feels defeating and is focused on my efforts, like where I went wrong, what I missed, how I could do better in the future. I kind of want a formula or process I can follow to guarantee success and inherent worth. I repeatedly play back my failures and regrets, think about how much better and more successful other people are, and generally confront loads of thoughts I didn't even know I had. Even though it isn't exactly the same, you described your experience really well, and I definitely experience envy and shame quite prominently, but they feel very unfamiliar and scary.