https://doi.org/10.1177/0146167218798823 Personality and Social Psychology Bulletin 1–14 © 2018 by the Society for Personality and Social Psychology, Inc Article reuse guidelines: sagepub.com/journals-permissions DOI: 10.1177/0146167218798823 pspb.sagepub.com Empirical Research Paper After staying up late to study, a tired student fails her organic chemistry exam. At home, a tired man arguing with his wife strikes her out of frustration. Late at night, an elderly woman squanders her monthly paycheck playing blackjack in a casino. On the surface, these events seem very different; how- ever, they are all tied together through self-control. Self- control is the process by which people alter their mental states and behaviors to achieve desired goals in the face of goal- opposing temptations or distractions. Being able to success- fully enact self-control predicts a host of consequential outcomes, including less propensity to drink alcohol in excess, eat unhealthy foods, fight with romantic partners, and neglect responsibilities (Crane, Testa, Derrick, & Leonard, 2014; Hofmann, Rauch, & Gawronski, 2007; Muraven, Collins, Shiffman, & Paty, 2005; Simons, Wills, Emery, & Spelman, 2016). Because self-control is so critical to many important psychological processes, it is vital to identify fac- tors that shape self-control, including physiological factors such as sleep (Krizan & Hisler, 2016). Growing evidence indicates that inadequate sleep leads to self-control and these detrimental effects become especially disconcerting when considering that large portions of chil- dren and adults in the United States routinely fail to obtain adequate sleep (Barnes & Drake, 2015; Barnes, Schaubroeck, Huth, & Ghumman, 2011; Lanaj, Johnson, & Barnes, 2014). Thus, understanding the influence of sleep on self-control is also important for promoting optimal functioning and well- being. To advance this understanding the current study used data from a month-long daily diary to (a) replicate past find- ings where less sleep the prior night leads to next-day self- control difficulties, (b) examine a novel reason (i.e., perceived stress) for why short sleep leads to self-control dif- ficulties, and (c) explore who may be more or less vulnerable to this dynamic. How Does Sleep Affect Self-Control? One reason why insufficient sleep leads to self-control fail- ures involves amplified difficulties in exerting control over visceral and cognitive impulses. After a night of short or poor sleep, people are less able to restrain undesirable urges, such as stealing office supplies, cheating on tests, or insulting oth- ers (Barnes, Lucianetti, Bhave, & Christian, 2015; Barnes et 798823PSP XX X 10.1177/0146167218798823Personality and Social Psychology BulletinHisler et al. research-article 2018 1 Iowa State University, Ames, USA 2 Loyola University Chicago, IL, USA Corresponding Author: Garrett C. Hisler, Iowa State University, W014 Lagomarcino Hall, Ames, IA 50014, USA. Email: hislerg@iastate.edu Does Stress Explain the Effect of Sleep on Self-Control Difficulties? A Month-Long Daily Diary Study Garrett C. Hisler 1 , Zlatan Krizan 1 , and Tracy DeHart 2 Abstract Insufficient sleep is linked to increased stress and suboptimal self-control; however, no studies have examined stress as a reason for why sleep affects self-control. Moreover, it is unknown if there are individual differences that make people vulnerable to this dynamic. Daily diary entries from 212 university students across 30 days were used in a multilevel path model examining if stress explained how prior night sleep affected next-day self-control difficulties and exploring if individual differences in sleep duration, stress, or self-control qualified this effect. Increased stress partially mediated of the effect of reduced sleep duration on increased next-day self-control difficulty. Moreover, short sleep increased next-day stress more for individuals with higher typical stress. Daytime stress especially amplified self-control difficulty for individuals with shorter typical sleep duration. Findings implicate stress as a substantial factor in how sleep loss undermines self-control and identify individuals particularly susceptible to this effect. Keywords sleep, self-control, stress, personality, diary Received March 14, 2018; revision accepted August 13, 2018