I find I'm most challenged by things I really care about, because I really want to do them well. It causes quite a bit of anxiety. But that very thing you're afraid of is kind of like a blessing in disguise. If you didn't have that fear, you wouldn't have the other side - courage and bravery, positive emotions. As an actor, you get used to those fears, and you're almost happy when they show up. It makes you learn your lines and prepare.
The man who has ceased to learn ought not to be allowed to wander around loose in these dangerous days.