self-confidence, language learning and success in life

Do you think that there is a close relationship between self-confidence and language learning? I personally feel that those who are more self- confident are also more likely to learn a foreign language better than those who lack self- confidence and self-esteem.
I have been studying English since I was eight , now I am twenty-three, which means I have been learning it for fifteen years and yet I cannot see any progress which is embarrassing and frustrating at the same time. I consider myself to be a very shy person and my lack of self-confidence prevents me from seeking new and original ways that could help me improve my skills.
I think that self-confident people are more successful in learning a new language (and in life in general ) because of their positive response to a bad event which may occur in their lives ;they are more inclined to learn from their mistakes thus resulting in personal growth. Moreover, they look on the bright side of life giving importance to both positive and negative experiences.
However, this is my personal opinion which is not based on scientific evidence! What do you think?