Self-confidence is not congenital, but evolves as an essence of the myriad life experiences that we go through. To say that it determines the course of your life, would not be an overstatement.
However, there are some people who just refuse to trust their own capabilities and end up being weak and consequently unsuccessful. If you are amongst those people, then it's high time you pull up your socks and embark upon the mission to boost your confidence.
So, if you think that you did not make quite an impression in the party or a meeting, then there are at least hundred other people who think the same thing about themselves.
Hence, do not even consider for a moment what others might think about you or of your certain shortcomings. Having said that, I do not expect you to turn into a completely reckless person with absolutely no consideration for anyone. It's just that you should not let others' perceptions about you come in your way of success.
Losers keep losing until they discover they too can be winners! The problem with people having low confidence is that they do not realize their own prowess and refuse to take up tasks that can change their lives. Also, they end up taking tasks, which have a high potential of failure, so that their own perceived feeling of being a 'loser' is re-enforced!
Take for instance, you really like a girl in your college and think that perhaps she too has a soft corner for you. But you hesitate to ask her out for the fear of rejection, this is when some other confident guy jumps at the opportunity and makes the best of it. You are then only left pondering about the if and only situations.
However, this might teach you an important lesson in life, and that is to try to give your best without bothering about the consequences.
However, it is important to remain resilient and unperturbed by little hitches life throws at you. Have faith in your abilities and continue to pursue your efforts with great patience.