All you need is experience. Specially on things you love to do, if you are not good at it, then definitely you have to accept that you will fail in discussions against those experienced people on that field.
If you want to build your conifidence, mingle with people who have strong character, you will know them once you face them and you talk to them, they are usually different and very vocal with what they want the people to know, they could express everything they feel. Learn from them
A character is always based on your own ability. And to strengten it, be more honest to yourself and to others. Add more education and gain more knowledge, be patient, be responsible for your mistakes, be persistent and believe in yourself.