Francesca Murphy notes the difference between stage and screen acting ( God Is Not a Story: Realism Revisited ):
“Our bodies are the locus of our unity or singularity; You and I are whole or one because each of us is a certain physical space. And so, the stage actor uses her body to make her character a unity, to as to project an integrated ‘stage image’ throughout a play. On the other hand, the projected image of the screen actor is unified by a cutting process into which he does not enter, as an actor: whereas the theatre actor makes herself a unified image, the screen actor is made one. Whereas the ‘image’ the theatre actor ‘finally finds and fixes in himself and in the performance, he never separates from himself as from a living, feeling, and speaking person,’ the ‘edited image’ which comes out of movie acting ‘has been subjected to a technical finishing process quite impossible of application to a living being.’”
(The embedded quotations are from V. I. Pudovkin, Film Technique and Film Acting .)