Confidence comes from NOT always being right... DO you know someone that always has to be right? Is that person you? People that always have to be right are not confident, they are actually insecure and being insecure is the opposite of being confident.
But from not fearing to be wrong... That is the key to confidence. We all want to be successful and being successful requires confidence and confidence comes from not fearing to be wrong.
There is no one that will always be right, yet there are those that never think there wrong. Don't be that person. Have confidence and do not fear to be wrong.