On the television or film set, the director just can't use expensive time to explain things to inexperienced actors who aren't at home in the medium. And if the actor isn't at home, he won't feel relaxed, and if he isn't relaxed the chances are good that he won't give a satisfactory performance. And that probably means he won't be asked back for a second try. The main thing the actor switching from the stage to film or video tape has to learn is, when acting for the camera, only a small part of what he communicates is done through words. So he has to learn to think about acting in a different way.