Writing, as represented in pop culture, is often shown in one of two ways, both a fantasy. It is either a lucrative vocation that affords free spirits a comfortable lifestyle where they are as relaxed or important as they like; or it is Serious Business, the purview of difficult but unquestionably great people. These are myths, and try as writers might to undo the damage, the myths persist because they are perpetuated by the same type of people, often about the same type of people: men, usually white, typically straight, always troubled. In Shirley, the new film out from director Josephine Decker, that archetype is transposed to a woman and given new, unsettling meaning. In Shirley, writing is perhaps neither honorable nor terribly…