Your feelings determine whether you are experiencing happiness and joy or sadness and misery. Your thoughts, words, and actions create your feelings.
When your thoughts, words, and actions are at their best, you will experience great feelings. Right now and every moment of your life, you have the free will to choose your thoughts, words, and actions.
Regardless of how you actually feel, you can choose to speak and act the way you would if you were feeling very self-confident.
Feelings are very important. But they are not the main thing. What you say and do with your life will make the greatest difference in who you are and what you accomplish. You can still speak and act self-confidently, even if you are not currently feeling self-confident.
Don't be limited by a down mood or a negative state of mind. It's possible to feel insecure yet act and speak with self-confidence. In my experience, when people consistently speak and act with self-confident patterns, they usually internalize the awareness that they are more self-confident than they feel.
(Self-confidence, chapter 14 – Artscroll Publications)