The 4th wall is a term given to pretending that there is a wall between the performer and the stage. The fourth wall is dangerous for several reasons. First, it disengages the audience. Watching live comedy is supposed to be different from watching it in a live venue. Comedians that get on stage and begin saying their pre-rehearsed lines without acknowledging the audience create a chasm between the performer and the audience. The audience disengages because it becomes extremely difficult to bond with a comedian that’s simply rehearsing lines they created in the past. An analogy would be trying to use pre-rehearsed pick-up lines as opposed to actually having a conversation. The levels of engagement are the same. With pre-rehearsed lines you place the emphasis on you, while knocking down the 4th wall makes the show more communal. This is why when you learn how to perform stand-up comedy they teach you to not be entirely in your head. Doing so disengages the audience.