Niflamol said:

Pardon me for asking. But what is the 4th wall you are referring to and why is so bad by braking it?

If you think of a traditional 3-camera television studio set, they usually build only three walls. The fourth wall is the wall you or the studio audience has to imagine is there. "Breaking the fourth wall" on purpose is like Frank Underwood talking to the camera in "House of Cards", but we're talking about doing it on accident, like seeing the edges of a set or a boom mic, something that takes you out of the illusion of what you're watching being a real thing.