When my sister was little, she was terrified of speaking in public. Before one school event, I told her I had overheard teachers saying she was the most confident student in her class.
It was completely made up. She believed me, gave the speech, and did well. Years later, she became a lawyer and is genuinely fearless while speaking. She sometimes says she always had natural confidence. I never correct her. Maybe confidence is occasionally just a lie someone believes long enough.