A big component of feeling insecure is the image of perfection that we create in our mind. When the voice in our head compares us to that image of perfection it concludes that we are not good enough. Buying into this comparison with an imagined self is what creates the feeling of not being good enough.
It’s kind of silly to determine that we are not good enough based on an imaginary image in our mind but that is what we do with our beliefs. I battled this myself. When I unraveled the core beliefs structure behind the not good enough agreements a whole world of duality was exposed. When it was exposed to common sense awareness it fell apart because it was made of non-sense.
The feeling of not being good enough is created because we believe in stories and images in our mind that are not true. If I can change it, then you can change it too.