A good reason to say “Yes” to things that scare you, things you’ve never done before, is that they’re only that scary the first time. After you’ve done it–no matter how well it went–you get to add that thing to your bag of tricks. Now you lead youth retreats. Now you write books. Now you moderate meetings.
It’s now among the things you do. Do well? Maybe. There’s enough value in doing it at all, though, to make “Yes” worth it when given the chance.