“…Within this model, the effects of a painful/provocative stimulus decline with repetition, while the opposite effect (the opponent process) increases (Solomon, ). As a construct, the ACS has found support in military (Gutierrez et al., ), undergraduate (Willoughby, Heffer, & Hamza, ), and adults in outpatient and inpatient clinics (Smith, Stanley, Joiner, Sachs‐Ericsson, & Van Orden, ). Research has repeatedly shown people's pain tolerance—one aspect of ACS—habituates over time and that pain‐related outcomes (e.g., pain tolerance, pain threshold) are higher in individuals engaging in self‐injurious behaviors (Koenig, Thayer, & Kaess, ; Milne, Kay, & Irwin, ).…”