
Forget The Camera
Good actors know how to put all their attention on an object outside of themselves and block out any and all distractions. In doing so they are able to work spontaneously on a moment to moment, impulse to impulse basis. They are able to "play" with an absence of self-consciousness. They know that their actions are reactions to how they are being affected by the other person. To achieve this "privacy" in a "public" situation they have to learn how to open up. Availability, susceptibility, vulnerability are necessary elements of the best acting. intellectual, pre-determined responses suggests that the actor is not "listening" to the other person, which leads to flat or over-the-top responses.
A story about the late Stanley Kubrick comes to mind. Kubrick a NY native, was born in the Bronx....