Your confidence is a balloon, and it's ready to burst. Add a little air for getting called in for an interview. Add a little air for researching common interview questions and practicing your answers. And then add a lot of air for truly feeling that, whoa, you are so perfect for this job and you know you're going to impress the heck out of your interviewers.
And then you go to the interview, call the hiring manager Paul instead of Pat and see your balloon of confidence immediately shrivel and sail away. Now, with a couple pitiful scraps of latex that used to be your balloon, you have to explain (concisely and eloquently) why you're a great fit for the position.
Take it easy. When you pump yourself up for an interview, you may quickly deflate after relatively minor goofs. And then you, the confident, near-perfect candidate, become frazzled and dejected.