When you're acting and directing, you're standing there acting with another actor, and you're trying to do your performance, and at the same time you're watching their performance, and making sure the lights are in the right place, and if the person is wearing the right wardrobe. All these things are going on in your head.
It doesn't matter who's directing, or who's doing the movie; there are a ton of things that can go wrong, and they do all the time. So you just have to figure out how to get through it, and then how the director finally puts it together, and then see what the audience takes from it. That's the most important thing to me.