Its all in the mind, my friend.
Every one including you , me and Bill gates is insecure to some extent!. Its not about how we are but how we manage. Courage, as Tolstoy said, is not absence but mastery of fear. Same analogy for insecurity. Psychologically this is called negativity bias and its inbuilt in all of us and its good!
This negativity bias is the motivating force for some of us, if not all. Its only matters from which side you hold a knife. You can take it as a distraction or as a motivation.
They are smarter because they work on their dumbness and get rid of it!. They really really work hard. You only, don’t know it and don’t see it!
Work hard and as I often say to all my students that the real secret is in books!
Just go on studying and making small progress and you will be amazed the tin just one month you can change “Z” in Zero to “H” as in Hero.
You are already a hero. You only need to discover it. Osho