"Public solitude", the actor's ability to appear "private in public", is a concept that Stanislavski pondered, and for which Strasberg developed an exercise based on Stanislavski's reflections. When the actor is on the stage, he is of course in a public theatre. But what he is doing on the stage should appear to the public to be private.
When the actor creates this sense of privacy, he does not go out "to join the audience", the audience comes to where he is.
Strasberg felt that the Private Moment exercise was not of value to actors who have no difficulty in involving themselves completely, without concern for the public, or for actors who love to do emotional things anyway, without regard for the public.
I have found in my workshop that all of the actors can benefit from the Private Moment exercise, and assign it to each of them at various stages of their development.
For this exercise, the actor is asked to do something on the stage that they do in life, but it is so private, that if someone walked into the room they would have to stop doing whatever it is.
Strasberg emphasized the difference between "private" and "personal" by pointing out that although some things a person may do are personal, the person may not stop doing them when someone comes into the room, and may at one time or another share the personal thing with someone. The private thing the person would not wish to share, and would stop doing if someone came into the room.
Picking such a private activity, which might be something as simple as dancing a certain way, or singing with abandonment, or cleaning the inside of the nose with an index finger, the actor practices at home, making the effort to become aware of the sensory aspects of the room, and the personal behavior associated with the private activity.
When the exercise is performed, the actor sensorally creates the same room, concentrating fully on recreating it on the stage, and then begins the private activity.
This exercise, if executed with success, can unlock keys to suppressed expression, and transform otherwise inhibited actors to a state of "public solitude".