Another "play" concept that Herzog describes is the "shift to the left" in play that results when someone experiences trauma. He describes play as the ego function that is involved with trying on, revising, and making meaning without primary attention to the constraints of reality in order to create the self in a manner that is permissive and allows multiple drafts. Herzog defines trauma as something that occurs when what happens or what does not happen overwhelms the ego's capacity to play—that is, to try on, take off, orchestrate, and reorchestrate experience. Trauma causes a regression or reversal of the developmental process, a "shift to the left." This regression results in play going from an activity that involves displacement and symbolic equivalent, to one of enactment, to one of interactive enactment in which the prescribed participation of another is required. Some of the vignettes show ways the child psychoanalyst participates in this directed play.