Of course, the actor may not always openly acknowledge his awareness of you, especially in a serious play, or one which leans towards realism, but the two of you are always in contact. This can never happen in the movie theatre. No film actor can alter his timing to wait for your laugh. No matter how seemingly spontaneous or realistic a film appears, it is a finished product, a preserved record of something previously done. It is set before you as a complete and predetermined whole.
Nothing can go wrong with it, unless the film breaks.
Even then, the film can be repaired and viewed again from its beginning. It has never happened exactly the same way before and it will never happen like this again. All sorts of things could go wrong, and often do. The actors could forget their lines or trip and fall down. The scenery could collapse.