The study aims to understand what makes a 'successful simulation', one that follows the planned sequence of events embedded in the simulated scenario, thus producing the intended learning path and learning outcomes for the participating students. The study is based on observations of 15 full-scale simulation sessions of acute trauma handling during inter-professional training of medical and nursing students. The study shows that the briefing preceding the simulation frames the students' emergent actions during the scenario by demarcating 'possibilities' and 'impossibilities' for actions during the exercise. This in turn defines what actions are 'appropriate' and 'inappropriate' when the scenario is enacted. The simulation exercises are emergent and co-constituted by the diverse participating, socio-material actors. The extent to which this socio-material assemblage manages to produce and maintain the enactment of the patient during the simulation signifies the success or failure of the intended learning path of the exercise.