"Performing for the Camera"?

When I say to some of my newer actors in class “stop acting”, they often respond that they are, indeed, in an acting class. So?

If you catch somebody ‘acting’ in a move, that actor is doing it wrong. The moment he’s caught ‘performing’ for the camera, the actor has blown his cover. He’s no longer a private character in a private world. Now he’s a highly paid actor on contract to speak these lines for the public. Good-bye illusion. Good-bye career."

—Michael Caine, Acting In Film: An Actor’s Take on Movie Making

So? Stop acting. Even in acting class!