One thing in common with the job I have now and the one I was hired for is that I wasn't sure if I could do either one. Each position I'd held before that was a pretty safe bet. These were scary.
As it turns out, though, jobs I don't know how to do are my specialty. It's satisfying to start a project I feel absolutely unqualified for and then become an expert. That's what I've done with the Craftstravaganza and MIX--read that link; it's an interview, and I wish I could find an online copy of our feature article where I talk about this exact thing w/r/t crafts (i.e. learning is exciting, mastery is boring)--and my absolute favorite part was figuring things out from scratch. Once that's done I get a bit bored and start to think of other projects that want doing.
failing to get complacent. Here is a great video about pushing yourself to experiment and learning from failure. This quote resonates with me: "whenever Picasso learned how to do something, he abandoned it." Good advice for creativity and careers.