https://www.vox.com/science-and-health/2018/9/5/17818170/work-fatigue-exhaustion-psychology "This is the greatest mystery of my adult life: How can I spend all day typing at a computer and go home feeling exhausted? How could merely activating the small muscles of my fingers leave me craving the couch at the end of the day? This question actually lies very close to one of the more hotly contested issues in psychology: What causes mental fatigue? Why is desk work so depleting?" At some point they mention willpower <sigh>. Doing things that are unpleasant or deeply repetitive and therefore boring take more energy than pleasant tasks I expect. NO matter how much willpower is applied. And then there's the issue of total energy available. No doubt as a one off many people can muscle through unpleasant tasks. And while there might be some room for psychological research here I think we'd learn more about fatigue from studying the biology.