I've been a Taekwondo instructor for nearly 25 years now, so while my own start in martial arts was a lifetime ago, the experiences are fresh because I've seen the same thing on so many people's faces over those years.
Generally I would say that beginners to martial arts classes come in three types:
I've never done martial arts before, I want to, but I don't think I can do what you guys do.
I've never done martial arts before, I want to and think I'll be really good, so let's get started.
I've done some martial arts before, I want to try Taekwondo and can't wait to get started.
By far most people fall in to the first category