<p>Emotion characteristics, like emotion intensity and perceived controllability, shape how individuals regulate their emotions. While the link between emotion characteristics and emotion regulation strategies seems clear for some strategies, findings are mixed for others. This study proposes that individuals are most likely to engage in emotion regulation at average levels of emotion intensity and controllability, and less likely at low or high levels (i.e., when emotions are either too weak to require regulation or too overwhelming to regulate). To test this hypothesis, we used data from a 60-day diary study in 79 adults (mean age = 22.29, <i>SD</i> = 6.08, 84% female), who every evening reported on emotion characteristics (emotion intensity and controllability) and strategy use (distraction, rumination, reappraisal, expression, suppression, relaxation). In addition to single strategies, we also examined emotion regulation strategy switching (i.e., the extent to which individuals varied their strategy composition). We replicate some linear findings, including that expression, relaxation, and rumination were used on days with more intense and uncontrollable emotions (for expression only). Importantly, we provide novel evidence for quadratic relations, where suppression and reappraisal were used on days where emotions were of average intensity and controllability, and less on days where emotions were less or more intense and controllable than usual. Moreover, individuals were more likely to switch to strategies they typically do not use on days where emotions were less or more controllable than usual. These findings highlight the value of moving beyond linear relations when studying emotion regulation dynamics in daily life.</p>