Self-confidence is a skill. A skill that can be learned.
You cannot be self-confident about “everything.” That would, in fact, mean overconfidence.
But you can be self-confident about the jobs and tasks, activities and actions, abilities and competences that you have practiced, repeated enough times, and had success with.
Self-confidence is believing that you can repeat these scenarios again perfectly.
Self-confidence is also a belief. A belief helps you persist on your path.
You cannot persist at “everything”; you can only persist at activities that you can work hard on and improve, repeatedly and endlessly.
Self-confidence is the use of belief and repeated practice turned into skill.
You cannot be skilled at “everything,” so you cannot be self-confident about “all things.”
Your self-confidence is your ability to believe and practice the jobs and tasks, activities and actions, abilities and competences you want to up-skill.
The challenging cycle of belief, practice, hard work, and gradual improvement are what manufactures self-confidence.