A lot of people wake up one day and say 'I'm going to be an actor.' It means nothing, thousands do it. Most have an abundance of training; but so often, it means nothing. The training helps, it gives you technique and tools; but it means very little if it doesn't go deeper.
When you cast an actor in a film; the résumé is important to some people and the look is definitely a factor; but you're looking for someone with a bit of wisdom, with a story in their eyes. Robert Downey Jr isn't just a man acting out scenes from a page; he's a carriage for something more meaningful. His comedy has a sadness to it and his darker scenes have a lightness to them. He's able to be in two places at once because that's how his life is. He doesn't just play what's on the page, he plays what's inside himself. He does this whether he's in a little indie film or in a superhero movie.
The thing about real life is that we are in ten places at one time. If I'm at a party having a good time; I'm also worried about my drunken friend in the corner, and I'm a bit sad that my friend who died 4 years ago can't be there and I'm also dreaming about a beach holiday. If it was a scene in a movie; a great actor would be in all those places but a bad actor would just be at the party.
And this is what you can't teach. Some actors just want the red carpet. Some are too aware of themselves. Some just want to escape their lives. But you want to cast the ones who don't have blank expressions and don't look at things from one perspective. You want performers who bring it all to the table.
The most successful actors often have an ease about them which we assume is because of their riches and celebrity, and I'm sure that's a part of it; but more than that I feel that they have mastered themselves. Becoming a great actor is a personal development project. The more you get to know who you are and what triggers your emotions, the better you'll be. The training helps, but a lot of it needs to be figured out by the actors themselves.
