People with self-confidence are free to speak and act in ways that enable them to reach their potential. On the other hand, people who feel insecure and lack self-confidence might limit themselves greatly.
No human being can know the full potential of another person. Nor can any human being know his own full potential. You don't need to know your full potential before starting to speak and act in ways that will enable you to reach more of your potential. You only need to take the next step forward.
You don't need to know your potential self-confidence before you begin to think, speak, and act with self-confidence. You only need enough self-confidence to take another small step. That makes the process sound much easier, doesn't it?