To most of us, the nearest television comes to being live anymore is when they say that a show was shot live in front of a studio audience. Of course that's still not live television, as the actors will still get a chance to re-shoot scenes and the show isn't being broadcast live out over the airwaves as they film it. Yet, hard as it may be to believe, that is something that used to happen all the time in television — shows would beam out to audiences un-edited and actors would run the same risks that their cousins in theatre did when it came to forgetting lines or being in the wrong place at the wrong time.
Although there were similarities between live theatre and live television, there were sizable differences as well. Live television was made to be performed for the camera, while live theatre is made to be played in a large hall with a live audience. If you don't think that makes much of a difference, think of what an actor has to do to make himself heard and seen from the fortieth row of the theatre. Then think of putting that same person in front of a camera and having him or her doing the exact same performance — it would look and sound ridiculous. His voice would be far too loud and facial expressions that look normal up on stage to people in an audience would look horribly exaggerated when captured by the television camera.
One of the hardest things to do is to take a live performance of any play and put it on the screen. To do it successfully usually involves re-staging it specifically for the camera instead of for the audience. To actually stage it for both and make it look convincing both on camera and for those in the audience is a very tricky proposition that not only requires particularly skilled actors, but a director skilled in editing camera shots live to ensure you get the right mix of television and theatre. Shooting flat with one camera - just opening the lens so you can see the whole set and all the action taking place on it - makes for both lousy television and lousy theatre, so you'd want to be able to cut back and forth between close-ups of central characters, mid-range shots to show the reactions of those in the immediate surroundings, and long-range shots to capture the fact that it is indeed taking place on a stage set.