3. Introduce variability of stimuli into exposure tasks by moving up and down a fear ladder randomly. Inhibitory learning theory suggests that clinicians should frequently vary the difficulty of exposure to stimuli to create a consistently high level of emotion, which has been associated with superior extinction learning. This guideline means that, instead of moving up a fear hierarchy or ladder in a systematic way from least to most difficult over time, and moving on to more difficult items after habituation to easier ones has occurred, clinicians should design exposures that will allow patients to achieve variable but generally high levels of fear or anxiety over the full course of an exposure.