Some bizarre elements used in recent English performances are so startling or threatening or shocking to audience sensibilities that the dramatic illusion is broken. The spectator becomes aware of himself as being in the same time and space as the element rather than relating to it as if it were only fictional. In such instances the viewer responds as he would to other real-world events.

Traditionally, a theatre performance consists of an illusion created out of various actual materials including sound, paint, furniture, the bodies of performers, makeup, etc. Care is taken not to call attention to these materials because focus on them would break the fictional-world illusion. An attempt is made to assimilate into the illusion everything that falls within the space and time delineated by the work, although occasionally a mistake may cause the actual material to break out of the illusion—for example if an actor obviously forgets a line or a chair accidentally falls over. Such disruptions of the illusion are obstacles to the spectator's psychic absorption in the fictional world.