Funny how we all place limits on ourselves. Even if unintentional or subconsciously, it's so easy to back off on certain tasks because of a knee-jerk "there's no way I could do that" or worse, "that's not my job".
Reflecting on every major transition in my career, I often think that -- had I truly known what the next step involved -- I would have probably not made the shift. Perhaps missing some of the facts can be a good thing.
When that's not the case, you have to consciously push yourself to up your game. It's hard; I know. Exceeding your grasp takes as much faith as facts, driven by the will to do more.
Stretch yourself beyond complacency. You will be amazed.