Zro is right, everyone lacks confidence in some area. This would include being insecure about sexual issues. For some people, such as myself, this would be because of a lack of experience. People usually gain confidence with experience.

I'm quite confident about my chemistry and math abilities. This is because I have spent a lot of time with these subjects and know I am good at it. I'm not very secure when it comes to speaking foreign languages like Italian and Spanish, because I don't have as much experience with those.