Why can't I ask her out?

I think what had happened was that you probably just got to nervous or afraid of rejection. Rejection is actually hard to take from boys and girls and it is usually the case because if you were going to ask someone whom you know is going to say yes than it won't be hard for you to ask but if your really not to sure of the outcome than you kind of dwell on the situation and your always having second thoughts. If your someone who doesn't care about getting rejected or isn't nervous or ashamed then go for it but if your a really sensitive person than make sure that the person you ask feels the same exact way as you for your own good. And don't wait to long either because you never know when your chance is going to slip away!

Its something new, practice on a friend or something someone you trust ya know that ain't gonna rat you out. Its just because it something new and ur nervous. Everyone goes through it. You just gotta do it and then you build that confidence. Practice in the mirror or with a friend so when it comes down to it it will come out more natural and smoother than if you don't. Its like a actor, you gotta recite your lines before you go on camera so its smooth and real. Cool?

Because you're worried about saying the right thing so you have a hard time knowing what to say first.