Many clients experiencing anxiety, anger or sadness believe that their “unpleasant” emotion will escalate and go out of control. Frantic attempts to control emotions—such as suppression, blaming the self or using substances—only verify the belief that the emotions cannot be tolerated. This chapter describes the nature of beliefs that emotions will hijack the self and escalate to dangerous levels, and indicates how the client and therapist can test these beliefs by setting up experiments. These experiments can include mindful detachment and acceptance in the moment of an emotion, cognitive reappraisal of the situation and changing the goals to see if current unpleasant emotions escalate out of control. Clients can keep track of emotional intensity and observe that the level of emotion—or the experience of an emotion—rises and falls during the course of the day.