Joan Didion had migraines, excruciating ones, which descended on her as often as once a week, leaving her “almost unconscious with pain” and forcing her to shut down and shut out the world until, like a terrifying storm, they passed. We’re aware of the details because she insisted that we be. She laid them out in an essay published in 1968, making certain that we understood her vulnerability. In another essay, she clued us into how innocent she was when she arrived in Manhattan in her 20s and how jaded she was when, years later, she returned to California, “the Golden State,” which she appraised through a filter not of sunshine but of dread. The Santa Ana winds were always in the offing. The earth could quake at any moment.